The invention discloses a rain-proof surveying and mapping auxiliary support device capable of automatically adjusting water balance, which comprises a casing and a supporting device, a balance rod is slidably connected in the casing, a notch is formed in the casing, the balance rod slides left and right in the notch, the upper end of the balance rod is fixedly connected with a platform, the surface of the platform is rotatably connected with a connecting rod, the end, away from the platform, of the connecting rod is rotationally connected with a fixing device, and screw rods are rotationally connected into the platform, the connecting rod and the fixing device. According to the rain-proof surveying and mapping auxiliary support device capable of automatically adjusting water balance, a third long rod and a limiting rod are matched with each other, and the end, away from the third long rod, of the limiting rod is rotationally connected to the surface of the supporting device, so that the moving range of the balance rod in the notch is limited, and the balance rod slides in the notch under the action of the gravity center and drives the platform to adjust the position automatically, so that the platform is always parallel to the horizontal plane, and the effect of automatically adjusting water balance is achieved.