In order to meet the demand of high precision image measurement of large object, a method of measuring large size target with wide field of vision by using fish eye camera image distortion is proposed. According to the polynomial approximation function of nonlinear distortion, the camera imaging model is established, and the camera parameters are determined through the stereo calibration plate; Move the camera along the optical axis to collect two images, and establish a measurement model to measure the size of the target to be measured. Through the measurement experiments of checkerboard and the geometric dimensions of a large building, it is shown that the method of directly using the distorted image proposed in this paper is superior to the traditional method of correcting the distorted image into a linear image, and has higher measurement accuracy and stability.