The invention belongs to the technical field of sports backpacks, and discloses a mobile phone arm bag for outdoor exercise. The mobile phone arm bag comprises a bag body, a main bag, an auxiliary bag, a placement bag, a rainproof bag, a binding belt and a sweat uptake layer; the bag body is composed of the main bag and the auxiliary bag, a waterproof layer made of polyurethane is arranged at therear end of the bag body, and a placement cavity is formed in one side inside the main bag. The sweat uptake layer is arranged on the rear side of the bag body, due to the fact that the amount of exercise is excessively large, the arm will sweat, and disengagement is caused; accordingly, the sweat uptake layer can have the sweat uptake effect, meanwhile, the bag can be disassembled for cleaning, the waterproof layer is arranged at the rear end of the bag body, the certain influence caused by sweating of the arm to a mobile phone is avoided, the placement bag is arranged on the main bag, the rainproof bag is arranged inside the bag, once it rains or clouds, the bag body can be comprehensively covered with the rainproof bag, the protective effect is achieved, a storage battery is arranged inside the bag body and can charge the mobile phone, the phenomenon that the mobile phone is powered off in the using process is avoided, and a compass is arranged on the auxiliary bag.