An improved device, for actuating a valve, comprises a housing and a gear train accommodated in the housing. The gear train includes a center gearset, a planet-pinion carrier, and an output internal gear. The center gearset includes a first external gear and a second external gear being coaxially fixed to the first external gear. The planet-pinion carrier is mounted around the first external gear of the center gearset, wherein a first bearing is provided between the center gearset and the planet-pinion carrier; at least three pinions are mounted at a bottom or inside of the planet-pinion carrier, the pinions being meshed with the first external gear of the center gearset. The output internal gear is mounted in mesh with the pinions, wherein a second bearing is provided between the output internal gear and the housing. The present invention is durable in structure and has a high transmission efficiency.