The invention relates to a transition metal olefin polymerization catalyst and a preparation method thereof. The catalyst comprises (A) transition metal compound with general formula (I) and (B) organo-aluminoxane compound, wherein M in the transition metal compound of the general formula (I) is a transition metal atom of the IVB family in the periodic table of elements; m is an integer from 1 to6, R1-R6 respectively are H, halogen, hydrocarbyl and the like; and n is a number meeting M valence state, X is halogen, hydrocarbyl and the like. The catalytic olefin (ethylene and propylene) has relatively high polymerization activity and excellent structure adjustability, and the activity of the catalyst can be adjusted and controlled by adjusting ligand structure and transition metal types (Formula I).