Plot-track association is the most important part in multi-sensor data fusion system. To improve the correct association rate, the infrared sensor is taken into the fusion system. The angle of infrared with high accuracy is fused with the range of radar with high accuracy. Thus the discrimination between the fused track and the real track becomes smaller and the accurate status estimation of the target is obtained. The algorithms for radar data association and for radar/infrared data association are discussed. The simulation is made to compare the performance of the two algorithms.