A kind of grass trimmer and its liftoff power cutoff mechanism, power cutoff mechanism that this is liftoff include the wheel tool of a wheel seat, the microswitch of an installation what wheel seat and an installation what wheel seat. Wheel tool includes that one can install to upper and lower displacement the wheel shaft of what wheel seat, one be arranged what wheel shaft and can the what idler wheel that drives wheel shaft to move down when leaving ground, and one from the propulsion arm of wheel shaft up projection, and propulsion arm can be driven by wheel shaft and open microswitch touching or be detached from change in displacement between microswitch. Cutter mechanism can be made to shut down immediately, so the safety in utilization of the utility model grass trimmer can be greatly improved so that the moment on ground is overturned or is lifted away from the inclination of the utility model grass trimmer through the design of liftoff power cutoff mechanism.一種割草機及其離地斷電機構，該離地斷電機構包含一輪座、一安裝於該輪座的微動開關，及一安裝於該輪座之輪具。輪具包括一可上下位移地安裝於輪座之輪軸、一套設於輪軸並可於離開地面時帶動輪軸下移之滾輪，及一自輪軸往上突伸之頂推桿，且頂推桿可被輪軸帶動而在觸動開啟微動開關或脫離微動開關間位移變化。透過離地斷電機構之設計，使得本新型割草機傾斜翻覆或被抬離地面的瞬間，會立即使刀具機構停止運轉，所以可大幅提高本新型割草機之使用安全性。
