A method for alternating between two control units of a train, comprising: recording power-on identification numbers of a first control unit and a second control unit of the train, wherein the first control unit is a control unit started in a case that the power-on identification numbers are odd, and the second control unit is a control unit started in a case that the power-on identification numbers are even; acquiring (S102, S201) a first power-on identification number of the first control unit and a second power-on identification number of the second control unit when the train is started; determining (S103, S202) whether the first power-on identification number is equal to the second power-on identification number; adding (S104, S204), if the first power-on identification number is equal to the second power-on identification number, an odd number to both the first power-on identification number and the second power-on identification number to obtain new power-on identification numbers, and starting a corresponding control unit based on parity of the new power-on identification numbers; determining, if the first power-on identification number is not equal to the second power-on identification number, whether an absolute value of a difference between the first power-on identification number and the second power-on identification number is 1, wherein the first power-on identification number being not equal to the second power-on identification number indicates that one of the first control unit and the second control unit is a newly installed control unit; adding, if the absolute value of the difference is 1, 1 to a smaller one of the first power-on identification number and the second power-on identification number, and starting a control unit of which the power-on identification number is added with 1; obtaining, if the absolute value of the difference is not 1, a creditable power-on identification number which corresponds to either one of a larger one, a smaller one or an average of the first power-on identification number and the second power-on identification number; synchronizing the first power-on identification number and the second power-on identification number with the creditable power-on identification number to obtain equal synchronized power-on identification numbers; and adding 1 to the synchronized power-on identification numbers to obtain processed power-on identification numbers, and starting a corresponding control unit based on parity of the processed power-on identification numbers. recording power-on identification numbers of a first control unit and a second control unit of the train, wherein the first control unit is a control unit started in a case that the power-on identification numbers are odd, and the second control unit is a control unit started in a case that the power-on identification numbers are even; acquiring (S102, S201) a first power-on identification number of the first control unit and a second power-on identification number of the second control unit when the train is started; determining (S103, S202) whether the first power-on identification number is equal to the second power-on identification number; adding (S104, S204), if the first power-on identification number is equal to the second power-on identification number, an odd number to both the first power-on identification number and the second power-on identification number to obtain new power-on identification numbers, and starting a corresponding control unit based on parity of the new power-on identification numbers; determining, if the first power-on identification number is not equal to the second power-on identification number, whether an absolute value of a difference between the first power-on identification number and the second power-on identification number is 1, wherein the first power-on identification number being not equal to the second power-on identification number indicates that one of the first control unit and the second control unit is a newly installed control unit; adding, if the absolute value of the difference is 1, 1 to a smaller one of the first power-on identification number and the second power-on identification number, and starting a control unit of which the power-on identification number is added with 1; obtaining, if the absolute value of the difference is not 1, a creditable power-on identification number which corresponds to either one of a larger one, a smaller one or an average of the first power-on identification number and the second power-on identification number; synchronizing the first power-on identification number and the second power-on identification number with the creditable power-on identification number to obtain equal synchronized power-on identification numbers; and adding 1 to the synchronized power-on identification numbers to obtain processed power-on identification numbers, and starting a corresponding control unit based on parity of the processed power-on identification numbers.