ing at the problem of inconvenient placement of a target in the measuring plane and the difficulty of making a large-scale target in wide-area monocular plane measurement system, a method of calibrating with small-size plane targets laid on a parallel plane is proposed. A parallel plane is selected as a calibration plane, a single small-size plane target is placed reasonably in a plurality of positions on the calibration plane for shooting, and a large-scale plane target is constructed by combining the photos and the nonlinear optimization method is used to complete the optimization of the internal and external parameters of the camera. Combining with the parallel constraint and the distance parameter, the homography matrix between the measuring plane and the image plane is obtained and then the wide-area plane measurement is realized. The precision model of plane measurement is established, and the distribution of precision in the measuring area and the factors influencing measurement precision such as the internal parameters, the installation angle and height of the camera are analyzed theoretically and experimentally. The experimental results show that the proposed method can effectively guarantee the overall measurement precision. In the calibration in a trapezoidal visual field with an upper line of 920 mm, a lower line of 1360 mm and height of 920 mm, the measurement error is lower than 0.6% in the measuring plane away from the calibration plane 200 mm. The distribution of errors in the measuring area is consistent with that of the precision model. This method is fully applicable to the wide-area plane measurement.