Nitrogen is essential for the growth and development of plants. Increasing nitrogen application to rapeseed promotes the accumulation of biomass at vegetative growth stage, increases seed yield and protein content, but reduces oil content at maturity stage. Oil is the target product of rapeseed. Thus, it is of great significance to explore nitrogen-efficient varieties with higher oil production when reducing nitrogen application. However, the identification of nitrogen efficiency in different periods of rapeseed and the relationship between traits in different periods have not been reported. In this study, biomass and oil yield were used as indicators to evaluate the nitrogen efficiency of overwintering and mature stages, and then we analyzed the relationship between traits in different periods. The comprehensive evaluation model of nitrogen efficiency at overwintering stage was established through the variation analysis, principal component analysis and membership function analysis of each biomass index under different nitrogen level at overwintering stage. The plant biomass and the fresh biomass were extracted as the comprehensive evaluation indexes of nitrogen efficiency at overwintering stage. Three high-efficiency germplasms under high nitrogen condition, seven low-efficiency germplasms under both nitrogen conditions, two high-efficiency germplasms under low nitrogen condition and six high-efficiency germplasms under both nitrogen conditions were identified. At the mature stage, four high-efficiency germplasms under high nitrogen condition, six low-efficiency germplasms under both nitrogen conditions, three high-efficiency germplasms under low nitrogen condition and four high-efficiency germplasms under both nitrogen conditions were identified by oil yield as nitrogen efficiency index. Combined with the identification results of the two periods, two high-efficiency germplasms (Jie 65 and Zhongshuang 11) under high nitrogen condition in the two periods, one high-efficiency germplasm (6024-1) under both nitrogen conditions, one high-efficiency germplasm (Soviet rapeseed) under low nitrogen condition, three low-efficiency germplasms (Xingxuan 2, Reaina II and Gisora) under both nitrogen conditions were identified. The further study showed that the correlation was not significant for the traits between overwintering and maturity stage under different nitrogen treatments. The above results will provide materials and theoretical basis for studying the mechanism of nitrogen efficiency in rapeseed and clarifying the important regulatory genes.