The invention provides a control device for a ratchet rotary engine which is characterized in that a square slide block controlling an intake compression auxiliary cylinder and a square slide block controlling a working exhaust casing which are equivalent to and matched with a catch ratchet of the compression auxiliary cylinder and a catch ratchet of a working exhaust auxiliary cylinder are arranged in a control cavity plate; the square slide block controlling the intake compression auxiliary cylinder and the square slide block controlling the working exhaust auxiliary cylinder are respectively fixedly connected with a square shifting block controlling an intake compression cylinder and a square shifting block controlling a working exhaust cylinder which are respectively fixedly connectedwith the catch ratchet of the compression auxiliary cylinder and the catch ratchet of the working exhaust auxiliary cylinder through a shaft of the intake compression auxiliary cylinder and a shaft of the working exhaust auxiliary cylinder; the square shifting block controlling the intake compression cylinder and the square shifting block controlling the working exhaust cylinder are respectively meshed with cams of a round drive plate which is fixedly connected with a main shaft. The control device for the ratchet rotary engine can accurately complete four operating strokes of the rotary engine, namely entering, compressing, bursting and exhausting. The control device for the ratchet rotary engine has the advantages of small friction coefficient, smooth operation and low noise without a reciprocating mechanism, and has the advantages of energy conservation, environmental protection and long service life.