A method of slicing printing color 3D object and a color 3D printing system; the method includes following steps: execute a slicing process to a color 3D object for obtaining a plurality of layers of slice objects; analyze one of the pluralities of layers of the slice objects for generating sintering control data and color control data; lay a layer of powder; color the layer of powder according to the color control data; sinter the colored powder according to the sintering control data for completing printing one layer of the slice objects; perform repeatedly above steps until all layers of the slice objects are printed and a color stereoscopic physical model is generated. The method can effectively generate a color stereoscopic physical model. In addition, because of the adoption of laser sintering technology, the color stereoscopic physical model generated by the present disclosed example has great strength.