Abstract: When mandril was pulled out from steel pipes rolled under high temperature, whorls was produced on the inner wall of the pipe and it would influence the inspecting precision of magnetic flux leakage testing system. The featurs and origins of noise signals were analyzed, a new method of combined software and hardware was put forward to impede the noise signals. Software and nonlinear compression method could effectively restrict and compress the noise signals. Experiments and practical applications showed that the new method could improve the signal to noise ratio remarkably over 20 dB.