The invention discloses an ultrasonic pesticide wastewater degradation device with variable reaction volume. The device comprises a reaction container, a liquid level switch, a controller, a multi-path switching switch component, a drive isolation module, a power amplification module, an impedance matching transformer, an ultrasonic signal generation module, a matching inductor and a plurality of energy converters, wherein the reaction container is provided with a reaction tank; the signal output end of the liquid level switch is connected with the controller and is arranged in the reaction tank; the energy converters are arranged on the reaction container and are arranged along the liquid level fluctuation direction side by side; the output end of the ultrasonic signal generation module is connected with the drive isolation module; the output end of the drive isolation module is connected with the power amplification module. By the ultrasonic pesticide wastewater degradation device with the variable reaction volume, pesticide wastewater degradation under different volumes can be met, moreover, the degradation capacity is also high, meanwhile, the damage of the energy converters caused by excessive heating can be prevented, and the cleaning degradation of pesticide wastewater is accelerated.