Abstract: In order to study the effect of Mo element content on the microstructure and properties of CoCrFeNi high-entropy alloy fusion cladding layer, CoCrFeNiMo_x(x=0, 0.5, 1.0, 1.5) high-entropy alloy coatings were prepared on the surface of Cr12MoV steel by using pre-positioned powder laser cladding technology. The surface morphology, microstructure, microhardness and wear resistance of the coatings were analysed by using optical microscope (OM), X-ray diffractometer (XRD), scanning electron microscope (SEM), microhardness tester and reciprocating friction and wear tester. The results show that under the experimental conditions of this study, good metallurgical bonding is formed between the CoCrFeNiMo_x high-entropy alloy coatings and the substrate, the surface quality of the coatings decreases with the increase of the elemental content of Mo, and cracks are formed on the surface of the fusion cladding layer when x=1.5. When x≤1.0, the cladding layer is a single FCC phase structure, when x=1.5, the phase structure of the cladding layer is transformed into FCC phase+BCC phase+σ phase. With the increase of Mo element content, the microstructure of the cladding layer is gradually changed from coarse dendrites to fine cellular crystals, the hardness of the cladding layer increases, and the friction coefficient and wear rate show a trend of decreasing and then increasing. For the surface morphology and wear resistance of the coatings, it exists an optimum value (x=1.0) for the addition of Mo element.