An Yb-doped double clad large mode area(LMA) fiber laser with a novel simple cavity configuration is demonstrated. This fiber laser system applies one end face of the fiber directly as a cavity mirror, which is fine polished after collapsing. Laser is obtained with the 4% feedback of the end face which has been polished at an angle of 0°, and mode-locking is achieved by using a semiconductor saturable absorber as another cavity mirror. The average output powers are 144 mW and 120 mW with the repeatition frequency of 68 MHz (the corresponding single pulse energies are 2.1 nJ and 1.8 nJ ), and the pulse widths are 9.9 ps and 4.8 ps,respectively. By increasing the pump power, stable multi-pulse outputs of 150 mW and 220 mW are obtained, which demonstrates the power energy of two and four pulses accordingly. Furthermore, by adding grating pairs inside the cavity, the output wavelength is tunable in the 1020～1080nm range.