【Objective】 In order to reveal the molecular mechanism of the formation of seed number per pod in Brassica juncea L. and Brassica crops, and lay a foundation for improving the yield and breeding of B. juncea. 【Methods】 In this investigation, 221 recombinant inbred lines (RILs) were engineered using the B.juncea L. The study aimed to analyze the additive quantitative trait loci (QTL), additive × additive epistatic effects, and genotype × environment interaction effects on the number of seeds per siliqua in mustard-type rapeseed across five distinct environmental settings. 【Results】 The analysis identified a total of seven additive QTL associated with the number of seeds per siliqua, predominantly localized on chromosomes A02, A03, A05, A08, B02, and B03 of mustard-type rapeseed. The magnitude of additive effects ranged from -11.642 4 to 4.524 6, with the most significant additive effect observed in qSS2-71 (-11.642 4), which also demonstrated the highest heritability at 14.44%. The remaining six additive QTL exhibited less pronounced additive effects and heritabilities. Moreover, the study detected seven pairs of additive × additive QTL interactions influencing the number of seeds per siliqua and their corresponding interactions with the environment. The effects of these epistatic QTL interactions ranged from -4.930 8 to 4.193 6, with the genetic effects of these interactions across different environments approximating zero. Broad-sense heritability of the number of seeds per siliqua trait was 80.98%, while the narrow-sense heritability was 30.98%. 【Conclusion】 Although the number of seeds per siliqua in mustard-type rapeseed is somewhat influenced by environmental factors, the additive effects governing this trait appear to be minimally impacted by the environment, and the epistatic QTL interactions are not substantial.