| In this paper, 49 rapeseed (Brassica napus L.)accessions were used to screening and identity the drought tolerance during different stages of germination, seedling, pre-flowering and post-flowering. Furthermore, the inheritance were studied by means of mixed model of major gene and polygene. The main results can be summarized as follows:1. The correlations between seed characters and drought tolerance simulated by polyethylene glycol (PEG6000) during germination period were investigated in 49 genotypes rapeseed (Brassica napus L.) accessions. The result indicated that fresh weight increase% after 5h imbibition correlated with drought tolerance characteristics in significant level and showed rapid water uptake may lead to higher drought tolerance at the stage of germination. Calibration models were established with data of drought tolerance ability at the germination stage and absorbed spectrum of calibration sets in rapeseed.A set of representative individual rapeseed samples were used to predict the model,and the results showed that it was feasible to determinate rapeseed drought tolerance ability at germination stage by near infrared transmittance spectroscopy,and it could be used in early generation selection of drought tolerance breeding program at the germination stage.2. Forty-nine genotypes were clustered into 4 different levels of drought tolerance based on the root and growth traits in response to drought stress during 30 days after sowing (DAS) until DAS100. 1, 25,16 and 7 accessions were classified as high drought tolerant,drought tolerant ,medium tolerant and sensitive, respectively. The traits of root volume, root fresh weight, above-ground fresh weight, biomass, above-ground dry weight, total dry weight at DAS100 correlated with the seed yield of seedling drought treatment in significant level, moreover, the traits of root volume, above-ground dry weight, total dry weight correlated with the drought tolerance index of seed yield, which showed DAS100 may be the optimum period of seedling drought tolerance identification. It was feasible to screening and identifying the drought tolerance of seedling stage under none drought stress condition.3. Different responses to pre-flowering and post-flowing drought stress were analysed and the drought tolerance were comprehansively evaluated. The result indicated that the 14 traits were significantly reduced by drought stress under both pre-flowering and post-flowering and the former has the more amplitude reduction. Forty-nine genotypes were clustered into 3 different levels of tolerance in each treatment based on the values of compreensively evalue. Principal component analysis showed that the stronger root and dry matter accumulation ability, the higher drought tolerance during pre-flowering and post-flowering stage.4. Genetic analysis using mixed inheritance model of major gene and polygene showed the three DAS100 drought tolerance related traits of root fresh weight, above-ground fresh weight, total fresh weight and three flowering stage drought tolerance related traits of root length, root dry weight, root volume had the same genetic pattern, which was dominated by one additive major gene plus additive-dominance polygene(model D-2). The major gene of the six drought tolerance related traits had no additive effect and heterosis. Hereditability of major gene (h2mg) in F2 population of the six traits was more than 75 %, it should be selected in preceding generations for drought tolerant breeding.5. The results showed that"irrigate(I)+ nitrogen (N)+gibberellin(G)"is the best drought recovery measure. The grey relational analysis showed that the above-ground dry weight, lateral root volume, number of raceme pod and seed per pod were significantly related with the yield in the treatment of"I+N+G". After drought stress, on the condition of irrigation and application of any one element of N, K, there will have an significant yield increase when applicate gibberellin.
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