The invention discloses a device for detecting a storage battery through timing discharge under PWM (pulse width modulation) control. The device comprises a DSP (digital signal processor), a PWM high-frequency signal circuit, a PWM low-frequency signal circuit, an on-off logic judgment circuit, an electromagnetic isolation circuit, an FET (field effect transistor) discharge circuit, a set current analog output circuit and a discharge current detection feedback circuit. According to the device, the DSP is utilized to emit high-precision PWM signals, meanwhile, fast on-off of multiple groups of FETs are controlled, so that the storage battery realizes output of constant current close to short circuit current instantaneously, and the performance condition of the storage battery is judged through rapid detection for a current peak and attenuation change by the DSP. The device can detect the storage battery at any stage in the life cycle, and with the adoption of the DSP, PWM control signal precision and current detection precision both guarantee accuracy of a detection result and universality of a detection range. Due to extreme short conduction time, little heat is generated, and repeated continuous detection can be realized.