Theory of the self-starting passive mode-locked Yb3+-doped fiber ring laser generating short pulses is presented. The ultrashort pulse Yb3+-doped fiber ring laser with all-fiber structure has been designed and turned out. Two 976nm LD pumped lasers are used as the pump sources and high concentration Yb3+-doped fiber is adopted as gain medium. Using the nonlinear polarization rotation (NPR) effect of the fiber, self-starting stable mode-locked pulse is obtained. The mode-locked threshold power of the laser is 260mW and the output power is 25mW. The center wavelength of the mode-locked pulse is 1056nm with 3dB bandwidth of 11.7nm at repetition rate of 20MHz. Comparing with the other structures of the fiber lasers, the structure we adopted is more efficient and has better stability.