The work aims to maintain the strength and surface finish of the cemented carbide after pretreatment and enhance the adhesion of the deposited diamond film. Vacuum heat treatment gaseous boronizing was proposed to the WC-Co by vacuum tube furnace. Then, the diamond films were deposited by hot filament chemical vapor deposition (HFCVD). The structure, morphology and film-substrate adhesion strength of the samples were measured by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), Raman spectroscopy, surface profiler and Rockwell indentation test. The boronization treatment of cemented carbide could be completed in a short time by vacuum heat treatment gaseous boronizing method to obtain a boride layer mainly composed of CoWB phase and with high temperature stability. The surface hardness was increased by 15%~20% compared with the samples without boronization treatment, and the maximum hardness was 2445HV. Compared with the two-step pretreatment of acid and alkali etching, the boronizing treatment was better to improve the film-substrate adhesion. When the boronizing temperature was 1000 ℃, the outward diffusion of Co particles from the internal substrate could be more effectively inhibited, the quality of the deposited diamond films was the best, and the film-substrate ad-hesion property was also more outstanding. The heat treatment gaseous boronizing provides a simple and efficient mean to pretreat the WC-Co, which has good repeatability and can be used for mass processing. The deposited diamond films after pretreatment have good film substrate adhesion.