This study utilizes an octadecanethiol (ODT) solution-based wet passivation method for InGaN-based metal-semiconductor-metal (MSM) blue light detectors, achieving significant suppression of dark current leakage and a notable enhancement in photoresponse sensitivity. After ODT surface treatment, the dark current of the device is reduced by 1~2 orders of magnitude across the 0~6 V bias range. Meanwhile, near the response band edge (440 nm), the light-to-dark current ratio of the ODT-passivated device increases by one order of magnitude, demonstrating markedly improved detection sensitivity. Photoluminescence (PL) measurements show that the band-edge emission intensity of the InGaN material increases by approximately 30% after ODT treatment, confirming the suppression of surface recombination. X-ray photoelectron spectroscopy (XPS) results indicate that the ODT solution effectively removes surface oxides and forms a sulfur-passivated layer, thereby reducing the density of donor-like surface defects and the associated dark current leakage. This study demonstrates that ODT treatment significantly suppresses both surface recombination and leakage defects in InGaN materials, leading to substantial improvement in the overall performance of the photodetector.