The present disclosure relates to a method for demodulating a frequency modulated signal of a PMA standard wireless charging device, including: (1) reading coil signals, sampling the coil signals, and counting cycles; (2) extracting a frequency change according to a change in a cycle count; (3) determining data according to the frequency change and a frequency duration and outputting the data; and (4) splicing the outputted data. With the method, a demodulation part does not require a complex analog circuit, and the highest frequency desired at a digital circuit part is only 4 MHz. Moreover, at this frequency, there is only a simple addition operation, and the main operating frequency is below 236 KHz.