A W alloy was used as an electrode to prepare a coating on a CrNi3MoVA steel substrate by means of electrospark deposition (ESD) technique. The mass transfer coefficient (MTC) from the electrode to the substrate was calculated through measuring the mass change by employing an electronic balance in air and in argon, respectively, and the morphologies, composition and phase structure were analyzed by utilizing scanning electron microscopy (SEM), energy dispersive X-ray spectrum (EDS) and X-ray diffraction(XRD). The results showed that the ambient gas has an obvious influence on the surface morphology, microstructure, phase structure and MTC of the ESD W alloy coating. Although the MTC in argon has a high value in the ESD process, the whole W alloy coating can’t keep thickening as the ball-like bulges grow up on the surface, which will make the coating rough with the deposition time goes on.