The invention relates to the technical field of hay mower blade machining, and discloses a machining method of a high-strength handheld hay mower blade. The machining method comprises the following steps: S1, cutter forming is carried out, molten steel in a molten state is injected into a mold, and cooling is carried out after the blade is formed; S2, cutting edge punching is carried out, and the cutting edge position is continuously punched multiple times; S3, thermal forming and heat treatment are carried out, specifically, a cutter is put into a heating furnace at the temperature of 1000 DEG C to be subjected to thermal forging forming, isothermal quenching is carried out for 10 minutes, and the hardness of the quenched blade is 40-45 HRC; S4, tempering is conducted, the temperature in the heating furnace is reduced to 500 DEG C at the speed of reducing 100 DEG C per minute, and tempering is conducted for 30 minutes at the temperature of 500 DEG C; S5, shot blasting is conducted, the cutter is put into a shot blasting machine to be subjected to surface polishing for 2 minutes; and S6, surface treatment is conducted, and the cutter is put into an electrophoresis device to be subjected to black electrophoresis. The problem of cutting edge breakage can be solved, the cutting edge strength is high, the process steps are shortened, the machining efficiency is improved, and the manufacturing cost is low.