Abstract: 【Objective】 Due to the fast development in molecular biology and biotechnology, a large amount of biological data is available to the genetic studies of important breeding traits in plants. Currently, there are many publications on genes effecting quantitative traits (or QTL), where QTL main effects, interactions between QTLs, and between QTL and environment were the major topic. Based on these studies, QTL can be dissected as a single Mendelian factor, fine mapped on chromosome, and finally be cloned. On the other hand, the phenotypic selection is still playing an important role in traditional plant breeding, where the breeding efficiency is low and the prediction is imprecise. 【Method】 QuLine is such a computer tool that is capable of defining genetic models ranging from simple to complex and thus can simulate breeding programs for developing inbred lines. Based on the results of simulation experiments, breeders may optimize their breeding programs and therefore greatly improve the breeding efficiency. 【Result and Conclusion】 In this paper, we first introduce the underlying principles of simulation modeling in breeding, and then summarize the application of QuLine in comparing different selection strategies, parental selection using known gene information, and the design approach in breeding.