Currently, the research on pseudospark switches triggered by laser mainly focuses on triggering by ultraviolet laser, and the physical triggering mechanism is generally considered to be photoemission. However, when the weakly focused ultraviolet laser irradiates the photoelectric material (target) in a low electric field environment, the seed electrons generated by the photoemission are very limited. To further reveal the physical mechanism of the switches triggered by the weakly focused ultraviolet laser, we established the test experimental platform for discharge of pseudospark switches triggered by weakly focused 266 nm ultraviolet laser. On this basis, the emission characteristics of seed electrons irradiated by laser were tested. The effects of laser energy, switch voltage, gas pressure, target material and irradiation position on the trigger characteristics of the switch were studied, and the source of seed electrons and their contribution to trigger were analyzed. The results show that when the laser is irradiated on the edge of the hole on the back of the cathode, the prompt electrons generated by the photoemission are not the main source of the seed electrons, and the ultrafast electrons related to the ablation plasma are the main source. Therefore, when the laser is irradiated on the edge of the hole on the back of the cathode, the material with low density and melting boiling point is more suitable as the target material for pseudospark switch triggered by weakly focused ultraviolet laser. According to the testing result, in this case, the operating voltage is -15 kV, and the pressure is 80 Pa (helium), the minimum laser energy of the switch with magnesium as the target can achieve stable trigger conduction is 2 mJ, which is much lower than that of copper (6 mJ) and molybdenum (8 mJ). In addition, under the same conditions, when the laser is irradiated on the inner wall of the cathode hole of the switch, the trigger delay and jitter are 36.9 ns and 1.41 ns, which are much lower than those when the laser is irradiated on the edge of the hole on the back of the cathode (116.4 ns and 5.39 ns).