The invention disclose a GaN-based multi-quantum-well laser epitaxial wafer with low V-type defect density and a preparation method thereof; the preparation method comprises the steps that annealingand surface cleaning are carried out on a substrate (10), and an n-type GaN layer (11), an n-type AlGaN limiting layer (12), an unintentionally-doped lower waveguide layer (13), an InGaN/GaN multi-quantum-well light-emitting layer (14), a p-type AlGaN electron blocking layer (15), an unintentionally-doped upper waveguide layer (16), a p-type AlGaN limiting layer (17) and a p-type ohmic contact layer (18) are grown on the substrate (10) in an epitaxial mode in sequence, wherein the InGaN/GaN multi-quantum-well light-emitting layer (14) comprises an InGaN well layer and a GaN barrier layer; andin growing the GaN barrier layer a TMIn source is pumped so as to inhibit the formation of V-type defects in the GaN barrier layer and eliminate the common V-type defects in the InGaN/GaN multi-quantum wells, so that the reverse electric leakage of the device is reduced, the absorption loss of the device is lowered, and the thermal stability of the quantum well is improved.