A linear motion system (1, 1a, 1b), comprising: a guiding member; a moving member slidably disposed on the guiding member, wherein the moving member and the guiding member together form at least one circulation path, and when the guiding member moves relative to the moving member, the moving member generates a linear movement relative to the guiding member; a plurality of rolling members (13a, 13b) accommodated in the circulation path; and a preload adjusting module (15, 15a) disposed on the moving member and comprising a preload assembly and a preload regulator (152, 152a); wherein the preload regulator (152, 152a) applies a thrust to the preload assembly to adjust a preload value generated by the rolling members (13a, 13b) and applied to the moving member, wherein the moving member comprises two nuts (12a, 12b), characterized in that the moving member comprises a carrier body, the carrier body has a through hole, and the nuts (12a, 12b) are individually disposed in the through hole, the preload assembly comprises an adjusting member and an adjusting rod, the adjusting member is disposed on one of the nuts (12a, 12b) and tightly fitted to a periphery of the nut (12a, 12b), the adjusting member is a ring shape and comprises two adjusting sub-members (1511a, 1511b) and at least a locking member, each of the adjusting sub-members (1511a,1511b) has a half-ring shape, and the adjusting sub-members (1511a, 1511b) are assembled around the nut by the locking member and one end of the adjusting rod is disposed on the adjusting member, the preload regulator (152, 152a) is disposed at one side of the carrier body facing toward the adjusting member. a guiding member; a moving member slidably disposed on the guiding member, wherein the moving member and the guiding member together form at least one circulation path, and when the guiding member moves relative to the moving member, the moving member generates a linear movement relative to the guiding member; a plurality of rolling members (13a, 13b) accommodated in the circulation path; and a preload adjusting module (15, 15a) disposed on the moving member and comprising a preload assembly and a preload regulator (152, 152a); wherein the preload regulator (152, 152a) applies a thrust to the preload assembly to adjust a preload value generated by the rolling members (13a, 13b) and applied to the moving member, wherein the moving member comprises two nuts (12a, 12b), characterized in that the moving member comprises a carrier body, the carrier body has a through hole, and the nuts (12a, 12b) are individually disposed in the through hole, the preload assembly comprises an adjusting member and an adjusting rod, the adjusting member is disposed on one of the nuts (12a, 12b) and tightly fitted to a periphery of the nut (12a, 12b), the adjusting member is a ring shape and comprises two adjusting sub-members (1511a, 1511b) and at least a locking member, each of the adjusting sub-members (1511a,1511b) has a half-ring shape, and the adjusting sub-members (1511a, 1511b) are assembled around the nut by the locking member and one end of the adjusting rod is disposed on the adjusting member, the preload regulator (152, 152a) is disposed at one side of the carrier body facing toward the adjusting member.