The invention relates to a uniform mixing device, in particular to a uniform gas-liquid mixing device used before an underwater mixed transportation pumping inlet. The uniform gas-liquid mixing device comprises a cylinder cover, an inlet tube, a liquid level sensor, a bracket, a backflow tube, an electromagnetic valve, a tank body, a secondary mixing cavity, a support shaft, blades, a triangular fixing rack, an outlet tube, a fixing tape, a gas guide tube, a gas collection cover, electric heating wires, a mixing cavity and a gas inlet hole, wherein the cylinder cover is fixed at the top of the tank body through a bolt and forms a sealed space with the tank body; the tank body is fixed on the bracket; the inlet tube is fixed at one end of the tank body and communicated with the sealed space inside the tank body; the backflow tube is fixed at the other end of the tank body and communicated with the sealed space inside the tank body; the electromagnetic valve is connected with the backflow tube through a flange. Due to the design idea of 'separating firstly and mixing later', gas-liquid separation of a gas-liquid mixture is carried out firstly, and mixing is carried out later, so that the gas-liquid mixing efficiency can be relatively high, moreover, air blocking can be avoided, a vapor mixture can be automatically eliminated, and the working intensity of use and maintenance can be alleviated.