Disclosed is a precast concrete element of a unitized curtain wall. The precast element comprises a front retaining plate, two side plates and a main connecting plate. Two sides of the front retaining plate are connected with the side plates respectively to form a 'U' shape, a semi-open internal space is encircled, the main connecting plate is arranged in the internal space, and the main connecting plate is connected among the front retaining plate and the side plates in a manner of being perpendicular to the front retaining plate and the two side plates. The precast concrete element serves as a fireproof structure of a building, and precast concrete can be produced in a professional concrete plant according to design size of the building, and is high in strength and capable of bearing weight of people or carried objects. The precast concrete element can be directly mounted on a building body through bolts extremely conveniently and rapidly without consuming a large quantity of galvanized plates and fireproof cotton, and construction progress is accelerated.