Photoelectrons plays an important role in the latent image formation process of silver halide materials, and the decay characteristic of photoelectrons are dependent on the structure of silver halide microcrystals to a great extent. In this paper, the decay spectra of free photoelectrons and shallow-trapped electrons were obtained by optics and microwave double resonance technology. The depth and density of electron traps in silver halide microcrystals were discussed. Moreover, using the lifetime of free photoelectrons, the optimal doping amount of shallow electron trap dopants was found by analyzing the distribution condition of electron traps in silver halide.