The invention relates to a ratchet wheel locking type impeller welding clamp with the auxiliary discharging function and a control method thereof. The clamp comprises a base, a center shaft, a clamping ring, a step bolt, a compression spring, an ejector pin, a clamp cover plate, a pawl, a torsion spring, tension springs, tension spring columns and a handle, wherein the center shaft is located in the center of the base, a spigot is formed in the base and matched with a clamping ring spigot, the clamping ring and the base are provided with the tension spring columns respectively and are connected through the tension springs, a screw hole is formed in the base, the step bolt is installed on the base, the handle is installed on the clamping ring, the clamping ring is provided with notches, the clamping ring and the clamp side pawl form a ratchet wheel self-locking structure, the ejector pin is arranged in the base, a compression spring is arranged on the ejector pin in a sleeving mode, the clamp cover plate is installed on the base and is provided with a through hole for one end of the ejection pin to penetrate through, and the lower surface of the clamp cover plate is in contact with a supporting universal ball. The clamp has the advantages that clamping is simple and fast, positioning is accurate, the welding quality is reliable, the surface smoothness is high, the rejection rate is zero, the production efficiency is high, and the labor intensity is low.