Abstract: Detection probability and false alarm probability are two of the most important performance index of an infrared search and track (IRST) system. Detection probability and false alarm probability were decided by the performance of system hardware and detection algorithm, etc. The influence factors to system detection probability and false alarm probability were analyzed in this paper; the model of relationship between pipeline detection, detection probability and false alarm probability was established; the influence of pipeline detection to system detection probability and false alarm probability were studied. The simulation was conducted and the experiment results were analyzed. The system total detection probability or total false alarm probability will increase when the single frame detection probability or single frame false alarm probability increase, respectively. If the pipeline length is fixed, system total detection probability and total false alarm probability will decrease when the number of required detection frames increase.