The research is intended to prepare CoCrFeNiMo high-entropy alloy containing refractory metal Mo on the low carbon steel, and do some researches about the microstructure and mechanical properties of this cladding layer, and then provide theoretical reference and the experimental example for the subsequent research of high melting point high-entropy alloy in surface engineering. Co, Cr, Fe, Ni, Mo metal powders were mixed evenly according to the equal molar ratio. And then the CoCrFeNiMo high-entropy alloy cladding layer was manufactured on Q235 steel by plasma cladding. The alloy components, crystal structure, microstructure and microhardness of this cladding layer were investigated by XRF, XRD, OM, SEM and microhardness tester. The results showed that due to the element burning phenomenon in the process of plasma cladding, the actual composition of the cladding layer was Co1.17Cr0.92Ni1.06Fe0.92Mo0.92. The cladding layer formed a good metallurgical bond with the substrate. The cladding layer was mainly composed of FCC phase with a small amount of σ phase. The microstructure was dendrite structure. Furthermore, the dendrite was FCC phase with a variety of elements, and the interdendrite was eutectic structure composed of FCC phase and σ phase rich in Mo and Cr. In addition, the phase formation law of high-entropy alloy was very complex and its phase structure could not be predicted only by thermodynamic parameters, but still needed to be verified by experimental results. Due to the solid solution strengthening of Mo element and the precipitation strengthening of σ phase, the hardness of the cladding layer was obviously improved, and the hardness of the surface was about 485HV. Therefore, the CoCrFeNiMo high-entropy alloy cladding layer is successfully prepared on Q235 steel by plasma cladding. The hardness of CoCrFeNi high-entropy alloy is improved by adding Mo.