We have developed a microfluidic chip for colorimetric Cu2+ detection. In this chip, it is facile to do colorimetric Cu2+ detection based on gold nanoparticles. This method has a dynamic detection range from 0.75 to 50 µmol/L with only 20 µL solution including detection reagents and sample. The result can be readout by naked eye and photographed by digital cameras. With the help of image processing software, we could measure the RGB value and calculate the Blue/Red ratio for more accurate quantification. Tap water could be detected in this portable chip.