Abstract: Reactor Monte Carlo code (RMC) was constantly developed for reactor large-scale precise analog calculation. In criticality calculation, the maldistribution of reactor neutron flux and power density lead to greater volatility in statistical bias, causing asymmetries in the computed results of reactor physical symmetry zones. Computation asymmetries in Monte Carlo codes are mainly caused by statistical variance, which can be reduced through decreasing variance volatility. In this study, uniform-fission-site method was added into RMC criticality calculation, with Hoogenboom-Martin benchmark verified by calculations. The result shows that the modified algorithm can significantly reduce the variance volatility of reactor cores and the variance of low power regions.