A compact continuous-wave blue laser at 488 nm, with the maximum output exceeding 20 mW at the optimum work temperature of crystal 28 ℃, is demonstrated by direct frequency doubling of a laser diode (LD) with a quasi-phase matched waveguide periodically poled lithium niobate (PPLN) crystal. The size of the crystal is 8 mm×1.4 mm×1 mm, and the waveguide section is 4.5 μm×3.5 μm, with 5.2 μm poling period. The temperature characteristic of the second harmonic generation (SHG) in the waveguide PPLN is investigated. The results show that the dependence of the waveguide PPLN crystal on the temperature is less than that of normal PPLN. Because the crystal works near the room temperature, the temperature controlling devices are simplified and the work efficiency of the whole system is improved. Based on the experiments, a compact all\|solid state 488 nm blue laser with continuous wave output is made.