The invention discloses an online 
monitoring system and a method for 
partial discharge of an intelligent switch cabinet based on ultra-
high frequency detection. The online 
monitoring system comprises a sensor unit, a 
signal conditioning unit, a MCU (Micro 
Control Unit) unit, a 
communication unit, a 
system power supply and an upper 
machine monitoring unit. The online monitoring method comprises the following steps that: the sensor unit finishes collection of 
partial discharge signals in the switch cabinet; the 
signal conditioning unit realizes amplification, filtering, 
frequency reduction and bias of the signals, thus obtaining signals which can be converted by an ADC (
Analog to Digital Converter) module in a DSP (
Digital Signal Processor); the MCU unit realizes analysis and procession of the signals; and data are uploaded to an upper 
machine in a monitoring room through an 
Ethernet. According to the online 
monitoring system and the method for the 
partial discharge of the intelligent switch cabinet based on the ultra-
high frequency detection disclosed by the invention, collection and procession of high-frequency signals conducted by the DSP are realized by adopting a 
frequency spectrum shifting technology; a time-
frequency analysis technology and a mode identification theory are applied to the monitoring 
system, therefore, the monitoring 
system is functional in fault diagnosis; and in addition, an IEC61850 standard is adopted by the system, consequently, management of various IEDs (Intelligent Electronic Devices) and interconnecting as well as networking of equipment in a 
transformer substation are convenient.