The free photoelectron lifetime reflects to a large extent the latent image formation efficiency and sensitivity of silver halide material. The microwave absorption dielectric-spectrum technique enables measurement of the photoelectrondecay process of silver halide emulsion exposed to 35ps laser pulse. For T-grain AgBr emulsion, the relationship between exciting energy and photoelectron action has been obtained, and the influence of iodide dopants on photoelectron lifetime was measured and analysed. The photoelectron lifetime of dye-sensitized AgBr emulsion with tabular grains is shorter than that with cubic grains, and the latent image formation efficiency of the former is higher than the latter.