The invention relates to a direct injection type real-time concentration variation on-line pesticidesmixing spraying device. The device comprises a water supply through-line module, a precision amount pesticide supply through-line module, a pesticide mixing applying module and a control module. The water supply through-line module and the precision amount pesticide supply through-line module are both connected with the pesticide mixing applying module. The control module is connected with the water supply through-line module to collect the flow and pressure signals of the water supply through-line module. The control module is connected with the precision amount pesticide supply through-line module to control the amount of the pesticides entering the pesticides mixing applying module based on the flow, pressure and the pesticide mixing ratio of the water supply through-line module. Water and pesticides are mixed in the pesticide mixing applying module, and sprayed out in time. The invention further relates to a control method for the direct injection type real-time concentration variation on-line pesticidesmixing spraying device. In the applying process, the injection amount of a variety of pesticides is controlled in a real-time mode, and the injected pesticides are mixed uniformly online. The device can be installed on any pre-mixing spraying machine, and has a simple and reliable structure.