Single crystal diamond film has been developed as high efficiency thermal management substrate, which has a promising potential in the field of wide bandgap semiconductor electronic devices. However, the slow production yield and rough surface of diamond film grown by microwave plasma chemical vapor deposition (MPCVD) make it unavailable as the substrate for semiconductor devices. In this work, single crystal diamond films were grown by MPCVD step by step, of which the growth rate was compared and the surface morphology and crystal quality was estimated by photos, XRD, AFM and Raman measurements. High-speed single crystal epitaxial diamond layer which could reach 20 μm/h with smooth surface was acquired by two-step growth technique of adjusting methane concentration. It is beneficial to solve the problems of rough surface morphology and processing difficulties of diamond epitaxial films in the subsequent fabrication of related electronic devices, so as to support the development of high power electronic devices.