The invention discloses a baud rate adaptive method for a universal asynchronous receiver/transmitter (UART), a device and the UART. The method comprises a step of measuring the width of the initial bit pulse of a received asynchronous serial signal with a preset clock cycle as a unit and obtaining the number of preset clock cycles in the initial bit pulse, wherein the preset clock frequency is N times of the least common multiple of all optional baud rates of a sending party, and N is a positive integer; a step of dividing the preset clock frequency by the number to obtain the transmission baud rate of the received asynchronous serial signal, a step of taking the transmission baud rate as the baud rate of the received asynchronous serial signal to receive the asynchronous serial signal. According to method, the device and the UART, the width of the initial bit pulse is measured through the preset clock cycle, the duration of the initial bit pulse is obtained, thus the baud rate of the asynchronous serial signal sent by the sending party can be obtained, and the asynchronous serial signal can be correctly received through an asynchronous receiving and sending transmitter with the transmission baud rate.