The present invention provide a detection circuit for frequency converter, the circuit comprises a switching input state decomposition circuit, the switching input state decomposition circuit is usedfor simultaneously generating switching characterization signals and line condition characterization signals based on output signals of a switching input circuit; a logic processing circuit, the logicprocessing circuit is used for performing logical operations on all of the switching characterization signals to generate unloading detection signals, and for performing logic operations on all of the line condition characterization signals to generate wire break detection signals; a switching output circuit, the switching output circuit is used for outputting the unloading detection signals andthe wire break detection signals to a following stage circuit for final transmission to the frequency converter. The detection circuit can transmit the signals required by the unloading function interface and the fault diagnosis interface of the frequency converter at the same time at a high speed, so that the unloading function of the frequency converter no longer needs take only one benefit between high speed and safety.