The invention discloses a time-varying control semisolid forming process. An alloy blank prepared in advance is heated to the temperature which is 40-60 DEG C higher than the solidus temperature for heat preservation for 20-60 s, semisolid slurry of a globular structure is obtained, and the liquid volume fraction is 25-35% at the moment; the obtained semisolid slurry is put into a mold, the temperature of a lower mold body of the mold is made to be equal to that of the semisolid slurry, the temperature of an upper mold body is controlled to be 300-350 DEG C, first section forming is conducted with the strain rate being 1.0-2.0/s until true strain reaches 0.4-0.5; and natural cooling is conducted after first section forming, after the liquid volume fraction is decreased to 10-15%, and secondary section forming is conducted according to a mold forming process so that the required deformation degree can be reached. The problems of nonuniformity of structures and unreliability of quality of formed magnesium alloy semisolid parts due to solid phase and liquid phase separation of existing semisolid forming processes can be solved.