A method for improving stability of large-particle-size latex subjected to pressure agglomeration comprises: adjusting the initial solid mass content of small-particle-size latex to be 35.0-42.5%, adjusting the pH value to be 8.0-13.0, adding an additive accounting for 0.05-0.5% by mass of dry small-particle-size latex; using a stirrer to perform mechanical stirring on the small-particle-size latex for 5-60 min before pressure agglomeration, and controlling the material charging temperature at 30-70 DEG C and the agglomeration pressure at 30-60 MPa; performing fusion processing on large-particle-size latex, and specifically adding a fusion agent into the large-particle-size latex accounting for 0.04-0.4% by mass of dry large-particle-size latex, wherein the fusion agent is acetic acid, potassium carbonate, sodium chloride or a mixture of multiple fusion agents. The method helps to improve latex precipitation phenomenon of agglomeration process, helps to realize continuous production, reduce energy consumption and equipment consumption wear, and helps to obtain the large-particle-size latex with uniform particle size and a stable system.