A FIFO device crossing a first and a second power domains is provided. The device comprises: a plurality of input registers belonging to the first power domain for receiving the input signal, and each of the input register having a first output; a first controller belonging to the first power domain for enabling the registers according to specific order and generating an initial signal; a multiplexer receiving the first outputs according to the specific order to generate a second output; a second controller belonging to second power domain, receiving the initial signal through an asynchronous interface and controlling the multiplexer to output second output; and an output register belonging to second power domain receiving the second output. First power domain operates according to a first clock signal. Second power domain operates according to a second clock signal. The first and second clock signals are asynchronous.