The invention discloses a high-dynamic-response oil flow rate measuring device and an oil flow rate measuring method. The high-dynamic-response oil flow rate measuring device comprises two sets of identical ultrasonic energy conversion devices which are installed at the two sides of a pipeline via a Z method. The drive signal input ends of the ultrasonic energy conversion devices are connected with the same drive signal generation device. The signal output ends of the ultrasonic energy conversion devices are respectively connected with the signal input end of a processing device. The processing device comprises a first filtering module and a second filtering module. The first filtering module is connected with the first input end of an analog-to-digital conversion module via a first operational amplifier. The second filtering module is connected with the second input end of the analog-to-digital conversion module via a second operational amplifier. The signal output end of the analog-to-digital conversion module is connected with the signal input end of the processing module. The signal output end of the processing module is connected with a display module. The high-dynamic-response oil flow rate measuring device has advantages of being high in dynamic response, short in sampling time and high in sampling rate so that solving of gas misoperation of an immersion type power transformer and arrangement of heavy gas setting values are facilitated.