This paper describes the method of using the optical telescope to assist the Tianma 13m radio telescope for pointing measurement and establishing the pointing error correction model. For small-aperture telescopes, there are few target sources for pointing and calibration, and it is difficult to establish a pointing model by radio method to cover the whole sky area. The Tianma 13m radio telescope of Shanghai Astronomical Observatory is used to conduct optical-assisted pointing measurement research. A set of optical pointing system was installed on the back frame of Tianma 13m antenna, which obtained a repeatable measurement accuracy better than 3$''$. In addition, through the analysis of the factors affecting the antenna pointing, a pointing error correction model containing 8 error terms, as well as the optical axis and electrical axis deviation models were established. The pointing model was brought into the antenna servo control system to cross-scan the calibration target radio source, and a pointing error of about 5$''$ was obtained. This research can provide a reference method for high-precision pointing modeling.