The utility model discloses a power supply detection circuit used for predicting residual life of a relay protection device. The power supply detection circuit comprises a power supply module, a backboard bus and a CPU module, wherein the power supply module is connected with the CPU module through the backboard bus, the power supply module comprises an electrolytic capacitor, an acquisition module used for detecting environment temperature of the electrolytic capacitor, a current sampling operation amplification circuit which is connected with the acquisition module, and a memory used for storing state information of the electrolytic capacitor, the current sampling operation amplification circuit is connected in series with an output loop of the power supply module, and the acquisition module and the memory are respectively connected with the CPU module. The power supply detection circuit realizes real-time estimation of residual life of the power supply module based on an aluminum electrolytic capacitor residual life prediction mathematical model and emits an alarm signal when a value of the residual life reaches an alarm threshold to prompt a maintainer for overhaul and replacement. The power supply detection circuit has properties of simple circuit, low cost, high reliability and strong practicality, improves reliability of the relay protection device and reduces maintenance cost.