The velocity mismatch would be inevitably in the push-broom imaging process based on time delay integration, which leading to a decrease in detection performance of point targets. Due to the lack of introduction of phase transfer function, the influence of the target detection performance can not be effectively analyzed by the frequency domain methods based on modulation transfer function. In order to solve this problem, the relationship between detection performance of point targets and velocity mismatch was studied with the establishment of the mathematical model by the point spread function and line spread function of the imaging system.The result of theoretical calculation and imaging experiment shows that the expectation of point target response will drop by approximately 50% by 8-stage time delay integration, when the velocity mismatch ratio ΔV/V=25%. When the velocity mismatch ratio ΔV/V=12.5%, the expectation of point target response decrease 30%.This research could provide reference for infrared time delay integration imaging system design.