Aiming at the problem that the binocular ranging technology has a large error in long-range ranging applications, this paper proposes a long-range binocular ranging method based on perspective transformation. First use the camera's internal and external parameters obtained from the calibration to perform stereo calibration on the distorted image. Use template matching to obtain the world coordinates of the four pairs of feature points and the distance of the selected baseline. The triangulation method calculates the distance between the target object and the camera. The experimental results show that when the object to be measured is 10m or more away from the camera, the traditional binocular ranging method has a large measurement error or even cannot be measured, and the perspective transformation method proposed in this paper measures when the object is 45m away from the camera. The error can still be guaranteed between 3% -5%, and the accuracy is high. Therefore, this method can effectively solve the problem of large error of binocular ranging technology in long-range ranging applications, and has certain practicability.