The invention relates to a data validity detection device for a transformer bushing monitoring system, which comprises a power supply and a transformer bushing analog device. The power supply provides a voltage for the transformer bushing analog device and a signal processor of the transformer bushing monitoring system receives a voltage signal output by a voltage measurement device and a current signal output by a current measurement device, calculates according to the voltage signal and the current signal to obtain a dielectric loss angle tangent measurement value and a capacitance measurement value and sends the dielectric loss angle tangent measurement value and the capacitance measurement value to a display for display so as to enable a worker to compare the dielectric loss angle tangent measurement value and the capacitance measurement value with a dielectric loss angle tangent actual value and a capacitance actual value which are set by the transformer bushing analog device and judge validity of data monitored by the voltage measurement device and the current measurement device of the transformer bushing monitoring system, thereby timely finding and maintaining the invalid transformer bushing monitoring system and ensuring the data monitored by the transformer bushing monitoring system to be accurate and valid.