Abstract: This paper introduces a new kind of colourless penetrant testing. Differing from the conventional colour contrast techniques and fluorescent techniques, the colourless penetrant it uses is a kind of environmentally friendly and transparent penetrant, so the testing process is simple and is of only two operations of penetrant and viewing. According to experiment and research, it is concluded that colourless penetrant testing is suitable for the inspection of surface shining components, and is high sensitivity for the detection of linear and planar imperfection.