The invention discloses a pile-pile connecting system and a construction method of the pile-pile connecting system. The pile-pile connecting system comprises a lower pile and an upper pile. The lowerpile and the upper pile are connected through a connecting piece. Multiple pre-embedded screw rods are arranged on the top of the lower pile. Multiple pre-embedded screw rods are arranged at the bottom of the upper pile. The connecting piece comprises a lower end plate, an upper end plate and ribbed stiffener. The upper end plate and the lower end plate are fixedly connected through the stiffeners. Multiple bolt holes are formed in the lower end plate. Multiple bolt holes are formed in the upper end plate. The pre-embedded screw rods on the top of the lower pile penetrate the bolt holes on thelower end plate and are connected with nuts, and the pre-embedded screw rods on the bottom of the upper pile penetrate the bolt holes in the upper end plate and are connected with nuts, so that pile-pile connection is achieved. According to the pile-pile connecting system and the construction method, the pre-embedded screw rods on the top of the lower pile penetrate the bolts on the lower end plate and are connected with the nuts, the pre-embedded screw rods at the bottom of the upper pile penetrate the bolt holes in the upper end plate and are connected with the nuts, up-down connection andfixing of multiple piles can be sequentially achieved, the connecting structure is firm, and the connecting operation is easy.