The invention relates to a synchronous mixing apparatus, which mainly comprises a jet flow mixer having a Venturi structure, a hydraulic control valve and an air pressure control valve, wherein negative pressure is generated in a gas suction mouth and a liquid suction mouth when a first liquid flows in the jet flow mixer, a button is pressed, the gas outlet end of a connection hole is communicated to a gas outlet mouth, the negative pressure maintains the communication state, an air pressure package is shrunk upward, a needle valve is lifted, a second liquid positioned in a second liquid container flows into the jet flow mixer through the gap between the needle valve and a needle valve seat, the inflowing second liquid and the first liquid flowing into the first liquid container are mixed to obtain a mixing solution having a uniform concentration, and the mixing solution flows into a mixing liquid container.