In the spectral domain optical coherence tomography (SDOCT) system, we can get high transverse resolution only within the focal depth field. The transverse resolution degrades away from the focal plane. Interferometric synthetic aperture microscopy (ISAM) is a three-dimensional image reconstruction algorithm, which can make the out-of-focus image clearer, and a resolution in all planes that is equivalent to the resolution at the focal plane can be obtained. At the same time, the contradiction between the transverse resolution and the imaging depth in the SDOCT system can be solved. The principle of ISAM and its possible applications are introduced and the comparison between the reconstructed images by the traditional SDOCT method and the ISAM is performed. The nonuniform fast Fourier transform (NUFFT) algorithm is applied in ISAM. Experimental results show that the NUFFT can greatly reduce the operation time, improving the performance of real-time and high-resolution SDOCT system.