The invention relates to a device and method for detecting voltages of a direct current bus of a variable frequency speed regulator. The device comprises a voltage dividing and current limiting clamping circuit, a differential input amplification circuit and a proportional amplification circuit. The voltage dividing and current limiting clamping circuit is used for converting the voltages of the direct current bus to millivolt-level voltage signals through voltage dividing and current limiting, and then introducing the millivolt-level voltage signals to the differential input amplification circuit. The differential input amplification circuit is used for amplifying and restoring the introduced millivolt-level voltage signals to volt-level voltage signals and then introducing the volt-level voltage signals to the proportional amplification circuit. The proportional amplification circuit is used for restoring the introduced volt-level voltage signals to actual values of the voltages of the direct current bus, and outputting the actual values of the voltages of the direct current bus to a control panel of the variable frequency speed regulator. Through the redesign of the device for detecting the voltages of the direct current bus, a detection circuit for the voltages of the direct current bus of the variable frequency speed regulator is simplified, the real-time performance, the stability and the precision of detection are improved, and a deviation correcting function is also achieved.