The selfstarting modelocked mechanism of nonlinear polarization rotation and the characteristics of the pulses were theoretically investigated with various parameters taken into account, such as gain, loss, group velocity dispersion, self phase modulation and fast absorber. A fiber ring laser with a small segment of highly Er3+doped fiber as gain medium, which is pumped by 980nm LD laser and modelocked by using the nonlinear polarization rotation technique, is successfully demonstrated for the generation of femtosecond pulses. When the laser was pumped at 23mW, stable modelocked pulses centered at 1552nm with 7.6nm bandwidth and an average output power of 0.43mW was successfully obtained at the repetition rate of 14.6MHz. The threshold power of the selfstarting modelocked pumping is about 11.5mW. The highorder stable modelocked pulses were also observed experimentally. Compared to the fiber lasers with the similar structures reported previously, the laser presented here has the advantages of very low selfstarting pumping threshold, high pulseenergy, small spectral sideband and better stability.