Developments in double clad fiber lasers, coupled with engineered nonlinear optical materials such as periodically poled lithium niobate (PPLN), are opening a way for a whole new class of practical nonlinear optical devices. Temperature characteristic and spectra characteristic of second harmonic generaration (SHG) in PPLN using quasi-CW broad band fiber laser have been investigated. The central fundamental wavelength dependence of PPLN temperature and the temperature FWHM phase-matching bandwidth were theoretically studied. The fundamental wavelength FWHM phase-matching of PPLN was calculated too. The 20 mm long PPLN with 6.5 μm poling period and 0.5 mm thick was used for doubling frequency of the quasi-CW broad fiber laser. The spectra of second harmonic at different temperature are achieved and discussed in detail.