The invention provides a trinuclear organic zinc catalyst, relates to a catalyst for lactide ring-opening polymerization, and specifically provides a bis(amidinate) ligand zinc complex catalyst with zinc as a central atom and a characteristic of N-C-N-Si-N-C-N. The preparation method comprises steps of: conversing a raw material of tert-butylamine to lithium salt by butyllithium under protection of nitrogen; adding cyanophenyl for an addition reaction; bridging by dichlorodimethylsilane to form a bridged bis(amidinate) neutral ligand; and carrying out a reaction between the ligand and diethylzinc. The synthetic method has advantages of general applicability, mild reaction conditions, simple and easily available materials, low price, simple steps and high yield. The compound has good catalytic activity on a lactide ring-opening polymerization reaction and promising application prospects.