Abstract: 【Objective】 This study aims to investigate the genetic effects of lambing traits COIL and BMPR-IB genes in the offspring of Duolang sheep and Hu sheep crossbreeding (Duohu sheep crossbreeding) cascade crosses by analyzing the association between COIL and BMPR-IB genes and the number of lambs produced. 【Methods】 Randomly selected F₁ (228), F₂ (254), and F₃ (252) generations of Duohu crossbred sheep were subjected to whole blood DNA extraction, and the COIL gene was genotyped using amplification refractory mutation system-PCR (ARMS-PCR) technique, and the BMPR-IB gene was analyzed in association with the number of lambs produced after genotyping using PCR-restriction fragment length polymorphism (PCR-RFLP) technique. 【Results】 In the Duohu F₁ sheep, the lambing numbers of the mutant pure GG type were significantly higher than those of the mutant heterozygous CG and the wild CC type (P<0.01), and that of the mutant heterozygous CG type were significantly higher than that of the wild CC type (P<0.01); in the Duohu F₂ sheep, the differences between the number of lambs produced by the mutant pure GG type and the mutant heterozygous CG and wild CC types were all highly significant (P<0.01); in the Duohu F₃ sheep, the number of lambs produced by the mutant pure GG and the mutant heterozygous CG types was highly significantly higher than that of the CC type (P<0.01), and the number of lambs produced by the GG type was highly significantly higher than that of the CG type (P<0.05). In the Duohu F₁, F₂ and F₃ sheep, the numbers of lambs produced by the mutant pure BB type were highly significantly higher than the number of lambs produced by the mutant heterozygous B+ type and the wild++ type (P<0.01), and the number of lambs produced by the mutant heterozygous B+ type was highly significantly higher than that of the wild++ type (P<0.01). 【Conclusion】 Both COIL gene and BMPR-IB gene have significant effect on lambing number of Duo and Hu crossbred sheep. However, the BMPR-IB gene has a low mutation rate in the progeny of Duohu sheep, which may not be suitable as a key gene for screening the double lambing population of Duohu sheep, and the COIL gene can be a new candidate gene for screening the high reproduction rate of Duohu sheep.