The invention discloses an outer control ultraviolet laser power stabilizing system, mainly for solving the problem that the existing laser power stabilizing system is low in stability. The outer control ultraviolet laser power stabilizing system comprises an ultraviolet laser light source system (1), an ultraviolet environment control room (2), an electrooptical modulator (22), a sampler (26), an optical chopper (3), an optical filter (4), a photoelectric preamplifying module (5), a feedback control module (6), an electrooptical modulation driver (7) and a laser power detector (8), wherein the ultraviolet laser light source system outputs ultraviolet laser power of which needs to be stabilized, the ultraviolet laser the power of which needs to be stabilized passes through the electrooptical modulator (22), the ampler (26), the optical chopper (3) and the optical filter (4) and vertically reaches an photoelectric detector to generate electric signals; the electric signals generate feedback signals through the feedback control module, to control the electrooptical modulation driver to adjust the electrooptical modulator to stabilize the ultraviolet laser power. The outer control ultraviolet laser power stabilizing system is high in stability, and is suitable for stabilizing the ultraviolet laser power with wave bands of 250-400nm.