A preparation method for modified molecular sieve and a modified molecular sieve-containing catalytic cracking catalyst. The preparation method comprises: mixing molecular sieve slurry, a compound solution containing ions of group IIIB metals of the periodic table of elements, organic complexing agent and/or dispersing agent and precipitating agent to obtain mixed slurry containing molecular sieve and precipitates of group IIIB elements in the periodic table of elements; and drying, and roasting or not roasting to obtain molecular sieve modified by the group IIIB elements. A weight ratio of group IIIB elements calculated based on oxides to molecular sieve dry basis is equal to (0.3-10):100, a molar ratio of organic complexing agent to ions of group IIIB metals is equal to (0.3-10):1, and a molar ratio of dispersing agent to the ions of group IIIB metals is equal to (0.2-16):1. Also related to is the catalytic cracking catalyst containing the modified molecular sieve prepared according to the method. The molecular sieve prepared by the method or the catalytic cracking catalyst containing same has good activity stability and heavy metal pollution resistance.