The invention relates to a sewage discharge diffuser preblending method and a high-preblending sewage discharge diffuser. The high-preblending sewage discharge diffuser comprises sewage inlet pipes, an annular pressure water chamber, a contraction pipe section, an isodiametric throat pipe section, a diffusion pipe section, a water sucking horn mouth and a water sucking main pipe section, wherein the contraction pipe section, the isodiametric throat pipe section and the diffusion pipe section form a coaxial communicating pipeline; the water sucking main pipe section of an inner sleeve is arranged in the water inlet chamber of an outer sleeve and is coaxial with the water inlet chamber to form an inner wall face and an outer wall face of the annular sewage inlet chamber; the water sucking horn mouth is arranged on the exterior of the outer sleeve, and the tail end of the contraction pipe section of the outer sleeve and the tail end of a pipeline of the water sucking main pipe section form a flow jetting spout. According to the sewage discharge diffuser preblending method and the high-preblending sewage discharge diffuser, sewage is jetted in a hollow rotating or non-rotating water jetting mode through the pressure generated when wastewater is drained, the negative pressure is formed in the hollow portion of the diffuser, environmental water is sucked into a negative pressure zone, jet flow carries the environmental water to be subjected to preblending mixing in the diffuser, the concentration or temperature of the wastewater is significantly decreased, and then the jet flow is drained out from a drain port of the diffuser; the area of a sewage discharge mixing area of the diffuser can be significantly decreased, and the environmental requirements are met.