The invention discloses an adaptive power grid signal fundamental wave detection method based on wavelet transform. According to an existing harmonic detection method based on wavelet transform, no unified determining standard exists for the number of wavelet decomposition layers. A system according to the adaptive power grid signal fundamental wave detection method comprises a spectrum detection module, a logical control module, a sampling module and a wavelet analysis module. The spectrum detection module extracts spectrum information in a power grid signal. After the logical control module acquires the spectrum information, an optimal number of decomposition layers in wavelet transform is determined according to an algebraic relation among the optical sampling frequency, the optimal number of decomposition layers and the lowest frequency band in wavelet transform. The sampling module performs power grid signal acquisition according to the optimal sampling frequency which is generated by the logical control module. The wavelet analysis module performs power grid signal analysis according to the optimal number of decomposition layers, wherein the optimal number of the decomposition layers is generated by the logical control module. The adaptive power grid signal fundamental wave detection method can adaptively and accurately determine the number of decomposition layers of the wavelet on the condition of processing a complicated power grid signal, thereby effectively improving extraction precision of fundamental wave information.