A tiny engine, in particular a tiny engine based on quasi - forces of gas flow circulating principle makes motor outputting power reach superhigh energy density. Tiny engine includes inner cam flywheel disk, slipper, cylinder body, piston rotor shaft, cover board, gas transmission mechanism and probe type spark plug. Said space in piston rotor shaft is premixing chamber for feeding high pressure gas fuel to cylinder body firing chamber, thereby realizing the thermodynamics effect through pre-set premix high pressure gas fuel form to substitute perfect gas power cycle constant entropy adiabatic compression process. Said invention has higher output loop net work, higher energy density and more simple system structure.