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This paper presents an improved median filter for ultrasonic image on time difference method as. Firstly, using the noise characteristics of randomness and incoherence, specially the impulse noise characteristics of short-time and great amplitude, however the characteristics of signal are certainty, continuity and relevance. The algorithm also can adjust the length of window adaptively and ensures its rationality and effectiveness in essence. At the same time, it uses the global median, global threshold and discrete move-window instead of the traditional continuous slide-window, simplified operand, reduced the computation time. In addition, instead of the traditional subtraction, the algorithm uses the results obtained by dividing the absolute value of initial data subtracts the median with the median as the condition for judging singular point, making the effective threshold have a selected range among the orders of magnitude and improving its operability and practicability. Finally, the simulation results compared with traditional median, show that the improved median algorithm is simple, quick and effective. It can remove the noise completely and retain the defect information perfectly.