The invention discloses a combination beam prestress application connecting structure and a mounting method thereof. The connecting structure comprises a plurality of combination plate unit pieces andsteel main beam unit pieces which are fixed to the combination plate unit pieces in one-to-one correspondence; each combination plate unit piece comprises a concrete plate; a plurality of horizontalpre-stressing tendons are arranged in each concrete plate; a pre-buried steel plate and high-strength bolts are arranged at the bottom of each concrete plate; adjacent two combination plate unit pieces are fixed through pouring; each steel main beam unit piece comprises a steel main beam top plate; the high-strength bolts penetrate through the corresponding steel main beam unit piece and the corresponding pre-buried steel plate to enter the corresponding concrete plate in sequence vertically. According to the combination beam prestress application connecting structure and the mounting method thereof, the prestress of the pre-stressing tendons can be directly, effectively and completely applied to the interior of the concrete plate skilfully and is prevented from being taken away, so that the bearing capacity of the concrete plate is improved, and the effect is remarkable.