The semi-solid ZCuSn10 alloy billets were prepared with strain induced melt activated (SIMA) method involved with hot rolling and reheating process. The microstructure evolution process and spheroidizing mechanism of α(Cu) phase were studied by means of optical microscope, scanning electron microscope and image analysis software. The results show that when a hot rolled ZCuSn10 copper alloy billet with a deformation rate 16% was reheated at 930℃, of which the semi-solid primary phase spheroidized gradually with the increasing holding time; while the average grain size of the copper alloy decreases firstly with time from 68.24 μm for 8 min to 62.31 μm for 10 min and then increases to 71.09 μm for 25 min; the liquid fraction increases from 18.14% for 8 min to 25.32% for 25 min; the shape factor decreases firstly with time from 2.91 for 8 min to 1.67 for 15 min and then increases to 2.43 for 25 min. The alloy exhibits the best semi-solid microstructure for 15 min holding with an average grain size 65.64 μm, a liquid fraction 23.66% and a shape factor 1.67. The microstructure evolution mechanism involves with merge of grains and growth as well as atom diffusion leading to grain growth and spheroidization.