The ANFO (ammonium nitrate and fuel oil) were modified by six kinds of surfactants including SDBS (sodium dodecyl benzene sulfonate),special expanded reagent, CTAB (hexadecyl trimethyl ammonium briomide),KH560 (γ-glycidoxypropyl trimethoxysilane), Tween80 (polyoxyethylent (80) sorbitan monooleate) and TX-10 (polyoxyethylene octylphenol ether). The SEM technique and the plate trace principle test method were used to study their particles microstructure and detonator initiation sensitivity. Results show that the effects of the surfactants are evident on both particles microstructure and detonator initiation sensitivity of ANFO. The modified ANFO with SDBS can not be initiated under detonator shock wave action,since its particle shows a sandwich shape with smooth particle surface and fewer pores. While other modified ANFO can be initiated due to their coarse particles surface and porosity.