In the 70° big visual field photoelectrictity measuring system,distortion produced by optical system makes the image of object in linear CCD deviate from the theoretical point and lead to the system measuring error. In order to improve measuring precision for the goal point in the measuring system,a set of device made up of eleven equidistance goal points for detecting optical distortion is designed on the basis of distortion theory. According to the change condition of systematic distortion,the compensation equation need fitting to join point location imagined by object point on linear CCD in real time measure. By the cubic equation fitting based on the data detected in measurement system as math model,the compensation program is compiled to carry out distortion correction in experiment program. The experiment result in actual detection shows that the device can reduce error obviously from -2.08 mm to 0.05 mm according to the compensation equation when the height is 200.115 mm,and raise the whole systematic detection precision from 1.039% to 0.025%.