A preparation method for a salt-spray-resistant polyaspartic acid ester includes mixing polyaspartic acid ester, cardanol resin and a catalyst together for transesterification reaction, and controlling a temperature at 100-130° C. and a relative vacuum degree at −0.095 MPa-−0.1 MPa, and stirring for reaction for 2-5 h to obtain the salt-spray-resistant polyaspartic acid ester; in particular, a molar ratio of the polyaspartic acid ester to the cardanol resin to the catalyst is polyaspartic acid ester:the cardanol resin:the catalyst=1:0.1-0.3:0.001-0.003, and the catalyst is tetraisopropyl titanate or dibutyltin oxide.