A mode-locked fiber laser using Semiconductor Saturable Absorber Mirrors （SESAMs） is one of the popular candidate seed light sources for the construction of picosecond pulse fiber amplifier. In this paper， the influence of the fiber length of a gain fiber， the reflectance of the Fiber Bragg Grating （FBG）， the modulation depth， the unsaturated loss， and the saturation flux of SESAMs， the mode field radii of single-mode transmission fibers and a single-mode gain fiber， on the output pulse characteristics， have been theoretically analyzed using the nonlinear Schrodinger equations. The characteristics of the pulse and the spectrum of an outputted laser have also been investigated theoretically. According to the simulation results， we built an ytterbium-doped mode-locking fiber laser system based on the non-polarization-maintaining linear cavity and a SESAM. Without any compensation for intra-cavity dispersion and external polarization control， a stable mode-locked pulse laser output has been achieved with the center wavelength of 1.06 μm， the pulse width of less than 12.51 ps， the spectral width of 0.32 nm， the repetition rate of 37 MHz， and the output power of 2 mW， respectively. The spectral edges of laser pulses appear smooth in our experiment， and the spectral distribution is close to the Gaussian shape. Finally， the overall structure of the near-infrared mode-locked fiber laser has been optimized by the systematic simulation. The mode-locked fiber laser introduced in this paper has a compact non-polarization-maintaining fiber structure， simple intra-cavity configuration with fewer components， high-quality output pulse correlation characteristics， which might provide a practical seed light source with the excellent performance for the next-generation picosecond pulse fiber lasers.