The invention discloses a preparation method of a non-metal-based photoelectric cathode. The method includes the steps of: 1) preparing graphdiyne through a solution chemical method; 2) calcining ureain a muffle furnace at 550 DEG C for 4 h to obtain a g-C3N4 bulk material; 3) dispersing the g-C3N4 bulk material in N-methylpyrrolidone and performing ultrasonic treatment for 20 h to obtain g-C3N4nano sheet dispersion liquid; 4) compounding the graphdiyne and the g-C3N4 nano sheet dispersion liquid through a solvothermal method to obtain the g-C3N4/GDY photoelectric cathode. The method overcomes a problem that in common hole-transport materials, an oxide containing metal is compound with g-C3N4 to prepare a non-metal-based photoelectric cathode. Under illumination, the g-C3N4/GDY photoelectric cathode has high light current responding value under -0.1V (vs NHE), which is higher than the g-C3N4 and GDY in single use by three times. The photoelectric cathode has high photoelectric catalytic activity and has simple preparation method.