The invention relates to an infrasound detection device and method of determining a goaf fire area in a coal field. The device includes an underground semi-space infrasound collecting and amplifying component/assembly, an infrasonic sensor, a preamplifier, a low-pass filter, a data recorder, a computer and a data transmission line. According to the infrasound detection device and method of the invention, ground semi-space signals are shielded through an internally-vacuumized double-layer hemispheric device; underground semi-space infrasound signals are received through the infrasonic sensor connected with the underground semi-space infrasound collecting and amplifying component/assembly; the output signals of the infrasonic sensor are transmitted to the preamplifier through the data transmission line; after being processed by the preamplifier, the signals are transmitted to the low-pass filter through the data transmission line, so that audio signals of which the frequency is higher than 20Hz are filtered out; the filtered signals are transmitted to the data recorder; data in the data recorder are inputted into the computer; and based on software calculation and analysis, the combustion fire area of the coal field can be located. The infrasound detection device has the advantages of simple structure, convenient operation and high detection accuracy.