The design of lightning current measurement system on Shenzhen Meteorological Tower is demonstrated, and the basic principle of the Magnetic-optic crystal sensor which is used to measure lightning current is introduced in this paper. First, the surge test about Magnetic-optic crystal is done, the results show that Magnetic-optic crystal sensor has a good time response performance and can record the lightning current waveform well. Besides, it also has a reliable measurement accuracy. Then it is applied to the current measurements of artificially triggered lightning tower in Conghua, Guangdong, China. The results of lightning current measurement between Magnetic-optic crystal sensor and coaxial shunt are compared. The analysis showed that the current waveform is generally consistent and the Magnetic-optic measurement can reflect the change of lightning current truly. Therefore, The Magnetic-optic measurement would be a good way in the measurement of lightning current.