This study describes an extra-cavity frequency-doubled kilohertz multiwavelength laser for an atmospheric detection lidar that uses an LD pulse end-pumped Nd∶YAG laser crystal. It adopts an electro-optic Q-switching technique and a compact metastable cavity design to achieve a high dynamic-to-static ratio of 1064-nm fundamental frequency optical pulse output. Type Ⅰ phase-matched LBO crystal frequency doubling and type Ⅱ phase-matched LBO crystal sum-frequency outside the cavity were used to produce 355-nm sum-frequency light. Additionally, the influence factor of 355-nm sum-frequency light pulse energy was theoretically and experimentally investigated. A three-wavelength laser beam splitting output with a repetition frequency of 1 kHz was obtained for a frequency doubling conversion efficiency of 53%. The corresponding single-pulse energy was 1.18 mJ at 1064 nm, 1.06 mJ at 532 nm, and 0.73 mJ at 355 nm, and the pulse width was 3.49 ns at 1064 nm, 3.42 ns at 532 nm, and 3.02 ns at 355 nm; and the beam quality factors were M_x² = 1.70, M_y² = 1.75 at 1064 nm, M_x² = 1.57, M_y² = 1.41 at 532 nm, and M_x² = 1.51, M_y² = 1.38 at 355 nm.