Through random simulation,the population size,the heritability of quantitative trait and the length of marker interval are investigated in analyzing the effects when using regression method for mapping QTL. The following results are obtained: (1) When the heritability is fixed, the accuracy of locating QTL increases as the population size increases. And when the population size is fixed, the accuracy of locating QTL increases as the heritability increases. (2) Whether the population size and the heritability are large or small, the mean of population and the additive and dominance effects can be estimated precisely by using regression method. (3) When the population size and the heritability are fixed, the significant test F decreases as the length of marker interval increases.