The invention discloses an energy saving method of a BBU (Base Band Unit) pool under a C-RAN (Cloud Radio Access Network) architecture, and belongs to the field of mobile communication. The energy saving method comprises the particular steps of: firstly, establishing a system model of users, RRHs (Remote Radio Heads) and the BBU pool; acquiring rates of transmitting the RRHs connected with a certain specific BBU to the users and a pre-coding matrix; calculating a transmission power usage rate rho trans and a traffic usage rate rho traff; then calculating a resource usage rate rho BBU of the specific BBU, and setting a kernel variable; pre-defining an upper limit and a lower limit of the resource usage rates of the BBUs, and defining four types of the BBUs; calculating the resource usage rates of all the BBUs in the BBU pool, carrying out partitioning according to four types and carrying out statistics on the numbers of various types; and finally, according to the kernel variables and the type numbers of all the BBUs in the BBU pool, carrying out switching among the BBUs to achieve energy saving. The energy saving method has the advantages that the resource usage rate of the specific BBU can be calculated and states of the BBUs can be dynamically switched; in the case of not influencing QoS of the users, one part of active BBUs in the BBU pool are closed and are enabled to enter a sleep state so as to save energy consumption.