Because of a very non-uniform power distribution in core region, a very non-uniform distribution of relative uncertainties exists for tallies in Monte Carlo criticality calculations of pin-by-pin reactor model. To make a large part of cells obtain small enough relative uncertainties with reasonable time costs, increasing the total sample scale is not a good choice. By realizing a modified uniform-fission-site algorithm on the basis of source iteration algorithm of parallel Monte Carlo transport code JMCT, we obtain higher efficiencies for tallies in the calculations of pin-by-pin model of the Dayawang reactor plant. This work supplies a useful tool for matching the goal of simulating the benchmark pin-by-pin reactor models with a pre-described standard(the so called Kord-Smith challenge).