With high peak power and good beam quality, it is easy for pulsed fiber lasers to trigger nonlinear process in a nonlinear crystal, and the near-infrared laser can be transferred into the ultra-violet or mid-infrared regime. In an experiment, the homemade high power pulsed fiber laser with central wavelength of 1064 nm and pulse duration of 650 ps is used to pump KTP (potassium titanyl phosphate) crystal, and the 532 nm laser is output after second-harmonic generation (SHG). In the process, the pulse width is compressed from 650 ps to 1 ps, the peak power density of the pump laser is raised to 24.97 GW/cm2, and the SHG efficiency increases from 0.8% to 8.4%. SHG efficiency is investigated for the pump laser of different average power, pulse width and beam spot, and the possibility to achieve highly efficient SHG with an oscillator is proved.