The utility model relates to an output circuit with a function of switching TTL (transistor-transistor logic) level into differential signal level. A first power source and a second power source are connected to a switch selecting end of an analog switch device N1, input TTL signals are connected to an enabling strobe end of the analog switch device N1, a switch output end of the analog switch device N1 is connected with a current-limiting resistor R1, a base electrode of an NPN (negative positive negative) triode V1 and a base electrode of a PNP (positive negative positive) triode V2 in series, collector electrodes of the two triodes V1 and V2 are connected with the first power source and the second power source respectively, emitter electrodes of the two triode V1 and V2 are connected to serve as an output end of the circuit to output differential signals after being connected with current-limiting resistors R2 and R3 in series. The output circuit has the advantages of simple structure and hardware resource conservation, stability in output signals, low vibration, excellent performance, high reliability, capability of properly selecting the analog switch device to realize one-channel or multi-channel output and flexibility in use and the like.