Spectral domain optical coherence tomography (SDOCT) is a new biological imaging technique. The traditional reconstruction method in SDOCT is based on Fourier transform. One disadvantage of this method is that the axial resolution of the system decreases with the increase of the imaging depth. A new reconstruction method is proposed which has the capability of maintaining the axial resolution over the all imaging depth. To prove the accuracy of this method, the cross-sectional images of the mirror and skin are obtained. The results demonstrate the effectiveness of the method. Compared with the methods reported, the new method has the advantage of not increasing the complexity of the system while having an almost constant axial resolution over the imaging depth.