The invention discloses a force transmission system in foundation pits on the two sides of a temporary even wall and a construction method of the system. The system comprises a plurality of first main beams, a plurality of first secondary beams, a plurality of second main beams and a plurality of second secondary beams, wherein the first main beams and the first secondary beams are arranged on one side of the temporary even wall alternatively, and the second main beams and the second secondary beams are arranged on the other side of the temporary even wall alternatively; the first main beams and the second main beams are arranged on the two sides of the temporary even wall in the same horizontal direction in a one-to-one correspondence manner, and the first secondary beams and the second secondary beams are arranged on the two sides of the temporary even wall in the same horizontal direction in a one-to-one correspondence manner; through holes are formed in the positions, where the first main beams and the second main beams are located, of the temporary even wall, and the first main beams and the second main beams are communicated in the through holes; and force transmitting structural steel is arranged at the positions, corresponding to the first secondary beams and the second secondary beams, of the two sides of the temporary even wall, and the first secondary beams and the second secondary beams are fixedly connected to the force transmitting structural steel on the two sides of the temporary even wall.