Metal-halide perovskites are recently extensively investigated as light absorbing material in solar cells. The outstanding optoelectronic properties and tunable light emission of the perovskites also make them promising candidates for light emitting diodes and lasers. However, understanding the relevant mechanisms and processes of the dependence of perovskite light emission on temperature and crystal size is still challenging. Herein, the CH3NH3PbBr3 monocrystals of different sizes are uniformly excited by two-photon absorption at 800 nm (100 fs, 1 KHz). In contrast to the reported relative large exciton binding energy (approximate to 76 meV) and spectrum clearly resolved excitonic absorption, the light emission origin in CH3NH3PbBr3 microcrystals at room temperature is unambiguously determined to be dominated by free electron-hole bimolecular recombination. The coherent light emission threshold of CH3NH3PbBr3 microcrystal increases with temperature, which is closely related to the temperature induced transition from exciton gas to free charge carriers. In addition, the coherent light emission threshold is found to decrease with the microcrystal size, which could be well interpreted by the interaction between the optical confinement, defect density, and cavity quantum electrodynamics effect. These results presented here may facilitate the development of perovskite light emitting diodes and lasers.