The invention discloses an on-line detection system and method for the droplet deposition during spraying operation of equipment for plant protection. The system is composed of a data processing module, a data collector, a temperature sensor, a spatial interdigital capacitance sensor, a communication module, a positioning module, a power supply module, a control end and other parts. The inventionprovides the spatial interdigital capacitance sensor with a three-dimensional structure, and the spatial interdigital capacitance sensor can output voltage data which is in direct proportion to the droplet deposition. The invention provides the specific method and steps for droplet deposition parameter detection. The method comprises the steps that the data processing module of the on-line detection system for the droplet deposition obtains the voltage data through the data collector and processes the voltage data output by the spatial interdigital capacitance sensor, and the voltage data is transmitted to the control end through the communication module. The detection system and method have the function of detecting the droplet deposition parameter during the spraying operation of the equipment for plant protection, and has the advantages of being high in adaptability, quick in response, high in detection precision and the like, and a reliable reference is provided for regulation andcontrol over the spraying operation of the equipment for plant protection.