The invention relates to a power control method for a fuel cell bus and a power system of the fuel cell bus. The power control method comprises the steps that required power P of the bus is acquired in real time; when the required power P of the bus meets the condition that P is smaller than Pfc, a fuel cell operates at Pfc, and a (Pfc-P) part charges a power cell; when the required power P of the bus meets the condition that P is larger than or equal to Pfc and is smaller than Pfce, the fuel cell operates at Pfce, and a (Pfce-P) part charges the power cell; when the required power P of the bus meets the condition that P is larger than or equal to Pfce, the fuel cell operates at Pfce, and a (P-Pfce) part is provided by the power cell, wherein Pfc and Pfce are two set threshold values of certain output power of the fuel cell. With adoption of the control mode, the output power of the fuel cell is prevented from frequent fluctuation and continuous loading and unloading, the durability of the fuel cell can be improved, investment cost is saved, and reliable operation of the power system is guaranteed.