Abstract: Pulsating laminar flow field in rectangular channel was investigated analytically. The influences of the flow fluctuation period, relative amplitude and aspect ratio on the flow field in rectangular channel were analyzed. The results show that velocity is composed of the steady component and the oscillating component at every point in rectangular channel. Compared with steady flow filed, the flow filed changes a lot under pulsating condition due to the oscillating velocity component, which leads to some change of velocity gradient in the near wall region.