The invention discloses a method for improving cavitation erosion resistance of TC4 titanium alloy based on ion implantation surface modification, and aims at improving the cavitation erosion resistance of TC4 titanium alloy, and expanding the applications of TC4 titanium alloy in the fields of hydraulic machinery, and naval architecture and ocean engineering. The method comprises the following steps of: placing the polished TC4 titanium alloy test sample in an MEVVA (metal vapour vacuum arc) source ion implanter, and using a high-purity niobium bar as an ion implantation source for performing Nb element ion implantation; and then performing a cavitation erosion experiment on the TC4 titanium alloy implanted with the Nb element, measuring the accumulated weight loss of the TC4 titanium alloy and observing the surface appearance after cavitation erosion. The results show that after the Nb element is implanted on the surface of the TC4 titanium alloy, the accumulated weight loss is reduced relatively to the accumulated weight losses of original test samples, and the cavitation erosion resistance is obviously improved.