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Adaptive filter based on least-mean-square (LMS) algorithm is used to pre-processing photoplethysmography (PPG) signal which is feeble and apt to affect by motion artifact. Firstly, relationship between normal signal and motion artifact is analyzed using Beer-Lambert Law for settling motive interference problem of pulse oximeter. It is shown that the disturbance signal and PPG signal is approximate linear combination relation, so signal processing methodology may be used to separate the two signals. And then adaptive filter fundamental is introduced and emphasized least-mean-algorithm that used in this paper. Random artifact and period artifact experiment validate this method at the end of the paper. It is shown that motion artifact is restricted effectively and able to compute with microcontroller.