An all-solid-state ultraviolet 244 nm laser by external cavity double-frequency is designed. Via V-shaped folded-cavity and actively Q-switched technique, the 914 nm and 1047 nm fundamental frequency beams pumped by the double diode arrays are used for intracavity sum frequency generation of a 488 nm high-frequency pulse laser. At the total pumping power of 44 W, the 488 nm laser output power is 527 mW. Using type I phase-matched BBO crystal, the 244 nm deep ultra-violet laser with an average output power of 28 mW is achieved. The repeat rate is 4 kHz with a pulse width of 17.8 ns, and the frequency-doubling conversion efficiency is 5.3%.