The invention discloses a serial communication system between devices and a method. The serial communication system between the devices comprises a master device, at least one slave device and an SPI (serial peripheral interface) bus for communication between the master device and the slave device. The SPI bus comprises a master-out slave-in signal line MOSI, a master-in slave-out signal line MISO, a clock signal line SCK, a chip selection signal line CS, a master transmission request and transmission completion signal line AP_RTS, a master reception preparation and completion signal line AP_RDY, a slave transmission request and transmission completion signal line BP_RTS, a slave reception preparation and completion signal line BP_RDY, a signal line AP_SLEEP for a master to awaken up a slave or control the slave to sleep, a slave sleeping state signal line BP_SLEEP and a slave abnormality state signal line BP_ERR. By adopting the system and the method, the transmission speed is high, and the cost of implementation is low. In addition, the system also has the functions of awakening up the sleep state and processing abnormalities, the failure in data communication in the sleep state of the slave device can be controlled promptly, the power consumption can be reduced, and the real-time monitoring of abnormal working states of the slave device can be achieved.