Abstract: The maize inbred lines PH 5 AD and PH 4 CV of Lancster group were used for cross combination, and four generations of continuous selfing were formed, namely S₀, S₁, S₂ and S₃.The inducer line H-4 was used to induce the hybridization of the above four generations.The results showed that there was a significant difference in induction rate among different generations, and the highest induction rate was 10.66% in S₀ generation.The haploid seeds of different generations were treated with 0.6% colchicine by bud immersion method. The results showed that different bud immersion time had a significant effect on the haploid doubling rate, and bud immersion time for 8 hours had the best effect, with the doubling rate of 19.91%. A diallel cross was formed between 20 DH lines from four generations and 5 test species from Reid group. It was found that S₀ generation had lower average combining ability in DH line. The general combining ability of DH line was higher in S₂ and S₃ generations, and the yield variation range of S₂ and S₃ generations was similar. The best generation to induce DH line was S₂ generation.