The invention relates to laser cladding nickel-based alloy powder and a preparation method thereof. The laser cladding nickel-based alloy powder is characterized by comprising the following components by weight percent: 0.2-0.7% of C, 2-3.5% of Si, 1.5-3% of B, 1.0-1.5% of Mn, 3-10% of Cr, 2-5% of W, 3-5% of Mo, 0.5-1% of Nb, 0.5-2% of Co, less than 15% of Fe, 0.2-0.4% of Y, 0.2-0.5% of Ce and Ni and the balance of unavoidable impurity elements. A manufacturing process flow of the laser cladding nickel-based alloy powder is as follows: burdening, smelting, atomizing, drying and sieving. The alloy powder used for laser cladding provided by the invention is corrosion-resistant and also has higher hardness, and a treated laser cladding layer has the advantages of no crack, no pore, no impurity, compact structure and refined grain. A large-area thick crack-free laser cladding alloy layer can be obtained without preheating or follow-up heat treatment, and the cladding layer has the advantages of high strength, hardness and abrasion performance, good plasticity and toughness and low cost.