The invention belongs to the technical field of an online dust concentration detection system based on a capacitor detection technology. According to the technical scheme, an analog-to-digital converter (2) is connected with a control unit (3), a capacitor sensor (5), a voltage\current converter (6) and an amplification unit (7); the control unit (3) is connected with a communication unit (4), the capacitor sensor (5) and the amplification unit (7); the capacitor sensor (5) is connected with the amplification unit (7); detection control software is installed in the control unit (3); a power supply (1) is used for supplying power to the analog-to-digital converter (2), the control unit (3), the communication unit (4), the capacitor sensor (5), the voltage\current converter (6) and the amplification unit (7). The online dust concentration detection system can be used for directly detecting the dust concentration on line, has the characteristics of high detection precision, high detection speed, convenience in use, high anti-jamming capability, safety and reliability, and also has the characteristics of small size, simple structure, short development cycle and suitability for various industrial severe environments.