Abstract: As a hole-to-electron converter doped in silver halide emulsion, formate ion can enhance photoelectron yield in latent image formation, trap the photogenerated holes, eliminate or reduce the electron loss caused by electronhole recombination in latent image formation process, and also release an extra electron to improve the photosensitivity. The decaying signal of photoelectrons generated by laser pulses in cubic AgCl and AgBr emulsions uniformly doped with different concentrations of formate ions was measured with the microwave absorption and dielectric spectrum detection technology. By the comparison of the decaying time and lifetime of photoelectrons, the influence of hole-trap effect of formate ions on photoelectron decay behavior in cubic AgCl and AgBr emulsions was analyzed, and it was founded that the optimal uniformly doping concentration was 10-5 mol/molAg.