The invention relates to a mobile energy storage power supply system control method applicable to a multi-access scene. The control method comprises the step of providing a two-stage on-line mobile energy storage power supply system, wherein an alternating current and direct current conversion part consists of two PCSs; an energy storage system is connected with a direct current side of the alternating current and direct current conversion part; interface types of the system and emergency power supply access include a single distribution network series interface, a single distribution network parallel interface and a double distribution network interface; for operating conditions to be applied, access precession mode setting of the mobile energy storage power supply system is divided into a single distribution network series type, a single distribution network parallel type and a double distribution network type; and different control methods are adopted. According to the control method, the mobile energy storage system can realize power supply guarantee operation on an important load under the different interfaces; charging and discharging optimization control is performed on an energy storage unit in the system by taking current energy storage quantity and an operating state of a grid side as considering factors; the power supply guarantee operation time is increased; the power supply guarantee capacity of the mobile energy storage system is improved; damage on a battery is reduced; and the service life of stored energy is prolonged.