The 4H-SiC films heteroepitaxially deposited on AlN/Si(111) substrates by chemical vapor deposition (CVD) are investigated in this work. X-ray diffraction (XRD), scanning electron microscope (SEM) and cathode illumination (CL) are used to analyze the structure characters, surface morphology and optics properties of the samples. The XRD spectrum shows that the SiC films have single (0006) orientation. The CL spectra indicates that the type of the prepared SiC films is 4H, and the CL efficiency of SiC films enhances with the increase of the growth temperature. It is found that lower substrate temperature is not beneficial for Si and C atoms to select the proper sites, leading to poor crystalline quality. While higher substrate temperature enhances the etching effect of H2 and desorption of absorbed atoms, which goes against the film growth. In addition, the ratio of C/Si influences on the growth of SiC as well. Excess Si results droplets on the surface, while excess C causes Si vacancies in the material. From these experiments, we point out that the preferred substrate temperature for 4H-SiC heteroepitaxy is between 1230 ℃ and 1270 ℃, the proper ratio of C/Si equals to 1.3.