A signal amplitude detection circuit includes a detector and a trimming algorithm module, and the detector having a preset baseline threshold reference value and an output terminal connected with the trimming algorithm module which is arranged for recording and decoding an output result of the detector to output an amplitude code value, and generating a control signal for controlling the baseline threshold reference value rise to a power supply level from a ground level or drop to the ground level from the power supply level, and the output result of the detector being “1” if a crossover occurs between the baseline threshold reference value and the detected signal; otherwise being “0”. The signal amplitude detection circuit detects the signal amplitude in a digital way, which has simpler structure, lower power consumption, reduced size of chips, and stable and accurate detection result without PVT drift.