The invention discloses an environment-friendly dispersed rosin size. The dispersed rosin size comprises the following components in parts by weight: 70-75 parts of rosin, 25-30 parts of modified rosin, 5-10 parts of a dispersant, 15-20 parts of a cationic emulsifier, 5-10 parts of an auxiliary emulsifier, 40-60 parts of a sucrose ester emulsion, and an appropriate amount of water. The invention also discloses a preparation method of the cationic dispersed rosin size. The method comprises the following steps: mixing rosin and modified rosin, and performing heating to be a melting state; addingpart of water for preliminary emulsification and cooling to 100-120 DEG C; mixing the cationic emulsifier and the dispersant, and then performing slow adding; and performing pre-heating mixing on theauxiliary emulsifier and the remaining water, adding to the mixture to make the rosin system change from a water in oil state to an oil in water state, and then adding the sucrose ester emulsion to obtain the environment-friendly dispersed rosin size. According to the method, the green and environment-friendly dispersed rosin size is prepared by adopting the high temperature normal pressure reversal process, using the cationic starch as the emulsifier and the synergistic action with the compound dispersant, and then adding the nontoxic and easily degradable sucrose ester emulsion prepared bythe normal temperature atmospheric pressure reversal process.