In cooling-type batch crystallization, the influence of undersaturation operation on crystal size distribution (CSD) was investigated by computational simulation. The model used considered the primary and secondary nucleation rates, size-dependent growth rate, and size-dependent dissolution rate limited by mass transfer; the crystal size dependence of the dissolution rate was determined by a Frossling-type equation. The population balance equation was directly solved by computational simulation by using the Cubic Interpolated Pseudo-particle method. The simulation successfully reproduced the order of the values of average crystal size in the experimental results for different temperature profiles. The model proved to be efficient for evaluating the influence of undersaturation operation on the CSD. In this paper, the influence of the frequency of introducing undersaturation, and the time at which undersaturation was introduced, on CSD was also discussed.