Asymmetrical Digital Subscriber Loop (ADSL) is suitable to eliminate "the last mile" bottleneck of current broadband solutions, which use the existing telephone network and apply more and more abroad. It results in the higher demands of the detecting equipment. According to the review and comparison of today "s ADSL detect instruments, a new method is put forward with the system design, which self - adapting detecting can be used to test the ADSLs transmission characters on the whole band dynamically. Current DSP is used to operate arithmetic. The self - adapting detecting arithmetic can get the characteristic of signal channel through the MATLAB simulation.