An unsteady stirring method, that is, coreverse rotation with different periodic intervals, was adopted to the suspension polymerization of styrene. Experiments were carried out in a 0.5-L flat-bottom flask with a six-blade Rushton turbine. Parameters affecting the final particle size and the particle size distribution under the unsteady stirring conditions, such as the agitation speed and the periodic interval, had been studied in detail, and the results were compared with those under a steady stirring one. The experimental results showed that the average particle size decreased and the uniformity final particle size distribution could be significantly improved when unsteady stirring approach is used. These were explained as the result of the decrease of the coalescence rate during the suspension polymerization when the unsteady stirring method was used.