A swept-source optical coherence tomography (SSOCT) system based on a high-speed scanning laser source at center wavelength of 1320 nm and scanning rate of 20 kHz is developed. The axial resolution is enhanced to 8.3 mu m by reshaping the spectrum in frequency domain using a window function and a wave number calibration method based on a Mach-Zender Interferometer (MZI) integrated in the SSOCT system. The imaging speed and depth range are 0.04s per frame and 3.9 mm, respectively. The peak sensitivity of the SSOCT system is calibrated to be 112 dB. With the developed SSOCT system, optical coherence tomography (OCT) images of human finger tissue are obtained which enable us to view the sweat duct (SD), stratum corneum (SC) and epidermis (ED), demonstrating the feasibility of the SSOCT system for in vivo biomedical imaging.