This study proposes a new method to limit the use of the quadrilateral model, which is applied in pyroelectric passive infrared sensor (PIR) arrays for target trajectory measurement. To this end, a triangle perception model using three sensing platforms equipped with a dynamic PIR array is introduced to measure the moving target trajectory. The single-sensing platform consists of four PIR sensors. The adjacent sensors are evenly spaced in the horizontal direction at 90., and the PIR speed is 10./s. Firstly, the three sensing platforms are arranged to form the triangle sensing model, and then, the angle information perceived by the PIR sensors from the three sensing platforms is filtered. Finally, the filtered effective information is combined with the sensing platforms’own coordinate information and time information according to the corresponding trajectory pre-rendering algorithm to derive accurate target motion trajectories and motion velocities. The experimental results show that the method overcomes the geometric constraints of the four sensing platforms, reduces the cost, and improves the accuracy of the prediction trajectory from 1.5 to 1 m. Thus, the proposed method has considerable theoretical significance and practical application value.