3C-SiC thin films were prepared by atmospheric pressure chemical vapor deposition. We performed a study on the effect of C/Si ratio on ferromagnetic properties and microstructures of 3C-SiC thin films. The 3C-SiC thin films show ferromagnetic behavior within the scope of C/Si ratio in our study. An initial increase in C/Si ratio leads to the enhancement of magnetization, while further increasing C/Si ratio reduces the magnetization. The ferromagnetism is associated with divacancy concentration in 3C-SiC thin films. Our study reveals that the ferromagnetism of 3C-SiC thin films is stable at room temperature, and this may be helpful for clarifying the current controversy of the ferromagnetism origin in diluted magnetism semiconductor.