The invention discloses an asynchronous over-level sampling analog-to-digital converter with a sampling threshold changing along with an input signal, and when the input signal continuously rises or falls all the time, the circuit changes the threshold of the whole design through the cooperation of a comparator module, a counter module and a digital-to-analog converter module. An external input signal triggers the output change of the comparator module, so that the binary value of the output of the counter module is changed, and the binary value change is translated by the decoder, thereby controlling the on/off of the digital-to-analog converter module and controlling the output voltage of the digital-to-analog converter module. The output voltage is connected with the reference voltage of the comparator module, and the threshold value of the design is changed by changing the reference voltage. Therefore, when the continuous and short-time input signals which rise all the time or fallall the time come, the circuit can reduce the sampling frequency according to the change of the threshold resolution, and the energy consumption is reduced.