The present disclosure provides asynchronous successive approximation register analog-to-digital converter (ASAR ADC) circuits and signal conversion method thereof. An exemplary ASAR AC circuit includes a sample/hold circuit configured to input a first analog signal and output a second analog signal; a digital-to-analog converter circuit configured to output a third analog signal; a first voltage comparison circuit configured to respond to a valid level of a latch signal, and output a first logic level and a second logic level; a first logic circuit configured to respond to a valid level of a flag signal, and identify a comparison result of the first voltage comparison circuit and output the first digit signal; and a pulse generation circuit configured to generate the latch signal and the flag signal with a generation time of the valid levels independently from the first logic level and the second logic level.