The invention discloses a double-rotor controlled alternate-running engine which can be slightly remodeled into a compressor and a pump. Two rotors inside a cylindrical cylinder are sleeved on a support shaft to be crosswise distributed, each rotor is provided with two fan-shaped pistons, rotor necks of the rotors respectively extend out of the cylinder, the rotors are sleeved with rotor gears, each rotor gear is provided with two sections of symmetrical short circular arc tooth deficiency, and a transmission shaft which is parallel to the support shaft and positioned out of the cylinder is sleeved with two transmission gears respectively meshed with the two rotor gears; the two rotors are respectively provided with a set of controllers mainly consisting of a control wheel and a reciprocating part, the rotor gears drive the control wheels to rotate, when the reciprocating parts are propped up, the combination position of the reciprocating parts and relative parts of the rotors is fixedly clamped, the rotors are restricted in the cylinder to stop rotating, the tooth deficiency positions of the rotor gears are just opposite to the transmission gears at the same time, and the transmission gears rotate without being interfered; when the reciprocating parts are in a motion state, the rotors are released to rotate, and tooth parts of the rotor gears are meshed with the transmission gears so that the power output is realized.