The electrode made of transparent semiconductor indium tin oxide (ITO) can reduce the edge current crowding effect of photoconductive semiconductor switches and improve the utilization of pulse laser. In this paper, 10 nm Ti and TiN layer were inserted into the interface between ITO and GaN, and the influences of Ti and TiN layer on the Ohmic contact performance between ITO and GaN were studied. I-V test results show that with the increase of the annealing temperature, the GaN photoconductive semiconductor switch with Ti insertion layer changes from Ohmic contact to Schottky contact, while the photoconductive semiconductor switch with TiN insertion layer keeps Ohmic contact characteristics. TEM observation shows that when Ti is used as the insertion layer, ITO diffuses through the insertion layer to the interface between the insertion layer and GaN, resulting in the formation of Ti oxide and holes at the interface. The transmission spectra show that the transmittance of samples with Ti insertion layer is less than 38.3% at different annealing temperatures, while the transmittance is 38.8%~55.0% when TiN is used as the insertion layer. Therefore, the photoconductive semiconductor switch containing TiN insertion layer shows a higher thermal stability and transmittance, which provides reference for the application of GaN photoconductive semiconductor switch in the field of high temperature and high power.