In this study, a collision method has been studied to reduce numerical error of Direct Simulation Monte Carlo(DSMC). In DSMC method, if the cell size is larger than the mean free path, the transport coefficient error occurs. Therefore, DSMC method has a rigorous constraint of the cell size to reduce the distance of a collision pair. To solve this problem, a collision model, the numerical error of DSMC is studied. Present model is changing the position of collision pairs to reduce the distance of a pair. Applying this model is a simple implementation by changing position of particles to be same. To account for physical validity of the model, mechanical, statistical consideration and error analysis have been done. To validate the developed code and the model, Couette flow problems have been simulated and analyzing the result has been conducted. Comparison with conventional results showed a good improvement.