Organic-inorganic 3D halide perovskite materials recently have become one of the major players of hybrid semiconductors for photovoltaic and optoelectronic applications.The diffusion length of charge carriers is one of the critical parameters for justifying photovoltaic applications of materials.In this work,we propose a realistic kinetic model in order to fully understand carrier relaxation rate of photoexcited organic perovskites with a negligible exciton formation in photoluminescence lifetime measurements.We find that the extraction of carrier relaxation rate has to be made from multiple fluence-dependent photoluminescence lifetime measurements with global fittings,instead of a traditional single-fluence lifetime measurement.To demonstrate the validity of the model,two kinds of p-doped CH3NH3PbI3 single crystals were grown up by intentionally increasing defects.Global fittings of the kinetic model to the two kinds of single crystals yield doping density,trap density,and recombination constants.Our methodology provides a self-contained approach to determine diffusion lengths of organic 3D halide perovskite materials.