A gravity power generation mechanism utilizes a gravity energy conversion unit to convert the gravity potential energy into the kinetic energy. The gravity energy conversion unit produces positive torques by adopting outward-spreading single directional swing arms and reduces the negative torques by cooperating with the folding action of the single directional swing arms, so as to perform a long-time, effective and continuous energy conversion of converting gravity potential energy into the kinetic energy. Next, the kinetic energy will be transmitted to a power generating unit to perform another energy conversion of converting the kinetic energy into the electric energy. And finally, a power supply system is used to transmit the electric energy out. By such arrangements, the gravity power generation mechanism not only has the advantages, such as: more simplified in structure, higher conversion ratio, and more environment-friendly but only needs a little of starting energy to perform a long-time energy conversion.