The invention discloses a portable cup lid and an assembly method thereof. The portable cup lid comprises a cup body and a portable lid, wherein the portable lid comprises an outer lid and an inner lid, pin holes are formed in the left side and the right side of the outer lid, metal pegs are inserted into the two pin holes, ring slots of the metal pegs are clamped into vertical clamp strips, and a cup handle is arranged on the two metal pegs in a sleeving manner. The assembly method comprises steps as follows: the inner lid is fed towards a cavity of the outer lid under pressure, and when the vertical clamp strips reach the pin holes, pressure feeding is stopped; the metal pegs are inserted into the left pin hole and the right pin hole of the outer lid after penetrating into end holes of the cup handle, and then the whole inner lid is pressed into the cavity of the outer lid; secondary injection molding is performed in a gap between the lower end of a drum ring and the lower end of the outer lid. According to the portable cup lid, the gravity is uniform, the hands feel comfortable, when the cup is used for water drinking, a cup handle can be taken down from the cup body with the portable lid, and obstruction caused by the handle is avoided.