The invention relates to cobalt-based alloy powder and a preparation method and application thereof. The cobalt-based alloy powder is prepared from, by weight percentage, 22-32% of chromium, 4-10% of molybdenum, 4-10% of tungsten, 0-1% of silicon, 0-0.75% of iron, 0-0.35% of carbon, 0.05-0.2% of nitrogen and the balance cobalt. The cobalt-based alloy powder is good in fluidity, small in particle size and concentrated in particle size distribution; the mechanical performance of a cobalt-based alloy material prepared through the cobalt-based alloy powder can reach the 5 type/type 5 of the GB17168/ISO 22674 requirement, the tensile strength reaches 1326 MPa, and the non-proportional extension strength reaches 948 MPa; and the elastic modulus reaches 206 GPa, and the fracture elongation rate reaches 13.8%.