Provided are a polyethylene polymer powder and method of producing the same that can improve molding efficiency while maintaining high levels of molded product strength and wear resistance. The polyethylene polymer powder comprises an ethylene homopolymer or copolymer and has an intrinsic viscosity IV of at least 12 dL/g and not more than 35 dL/g, a melting peak full width at half maximum of at least 2° C. and not more than 7° C., a span (laser particle size distribution measurement) of at least 0.9 and not more than 2, and an α-olefin content of 0 mol % to not more than 1.50 mol %. The method of producing this polyethylene polymer powder includes polymerizing ethylene or ethylene and an α-olefin by slurry polymerization using a loop reactor. In the polymerizing, supply of a solvent and ethylene or supply of a solvent, ethylene, and an α-olefin is performed by a plurality of supply lines.