Herein, a multi-wavelength defect detection system based on the theory of integral scattering detection is proposed. This system uses three light sources with wavelengths of 635 nm, 525 nm, and 405 nm and employs a photomultiplier tube as the photodetector. Two samples of high-transmittance quartz glass sheets with standard size defects,one with a width and a depth of 20 μm and the other with a width and a depth of 25 μm,are evaluated. The powers of the light source are 50 mW and 80 mW, respectively. Experimental results show that the highest scatter rate is achieved using the 405 nm light source. Therefore, the detection ability of the 405 nm light source is stronger than those of the 635 nm and 525 nm light sources. The findings of this study provide a reference for detecting small defects and achieving defect depth information.