A colorimetric method for the detection of traces of Cr(Ⅲ) was established by adsorbing methyl violet with N electron donor coordinating atoms on the surface of silver nanoparticles through bridging action and coordinate reaction,then the adding of Cr(Ⅲ) in the solution could lead to the precipitation phenomenon of silver nanoparticles sol,and followed by the solution color changing from bright yellow to grey red.Under the optimized conditions,the linear range for Cr(Ⅲ) was 2.0-10.0 μmol·L-1(r=0.997 6) and the detection limit for naked eye was 0.3 μmol·L-1.This method was applied in the determination of Cr(Ⅲ) in environmental samples,with recoveries of 93.2%-100% and relative standard deviations(RSD) less than 1.5%.It was rapid,sensitive and selective.