The present invention provides a data processing device and a method for switching states thereof. The data processing device comprises an operating system and a communication interface for communicating with another data processing device, wherein the communication interface is enabled when the operating system stays in the operating state of the operating system, and the communication interface is disabled when the operating system stays in a low-power-consumption state. The method for switching states comprises the following steps of: detecting whether the communication interface stays in the operating state of the communication interface and generating detection information; determining whether the operating system stays in the operating state of the operating system when the detection information indicates that the communication interface stays in the operating state of the communication interface, and generating determination information; generating a system state holding command when the determination information indicates that the operating system stays in the operating state of the operating system; and controlling the operating system to stay in the operating state of the operating system based on the system state holding command. The present invention can not only secure communication via the data communication interface, but also allow the operating system to handle normally and stably an interrupt, so as to reduce the system power consumption.