The invention discloses a limiting device of a plastic thread cover die based on hydraulic motor drive. The plastic thread cover die comprises a cavity and a bouncing-off device; a left thread separating insert and a right thread separating insert are arranged on the outer side of a rear die insert, a left gear is arranged at the lower end of the left thread separating insert, a right gear is arranged at the lower end of the right thread separating insert, the left gear and the right gear are engaged, and the limiting device further comprises a limiting gear; the limiting gear is engaged with the left gear, a limiting groove is formed in the limiting gear, the lower end of a limiting block is inserted in the limiting groove, the upper end of the limiting block is hinged to the outer side end of a raising plate through a long round hole, the inner side of the raising plate is hinged to a limiting elastic block through a long round hole, an elastic block spring is arranged below the limiting elastic block, and the static position of the limiting gear is the thread starting position of a plastic thread cover; and the limiting device of the plastic thread cover die based on hydraulic motor drive can effectively the problems that limiting is difficult, excessive screwing happens, and the size of a power source is large.