The invention relates to an energy storage converter based on a virtual synchronous machine and a control method thereof. A constant-voltage floating charging controller is added into an energy storage converter control system. The output quantity of the constant-voltage floating charging controller is used as a reference value for controlling the active power of the virtual synchronous machine. The constant-voltage floating charging controller is set according to the state of the energy-storage controller. When the energy storage converter is in a charging state, a difference between the real-time difference of the battery voltage and the constant-voltage floating charging voltage preset value is calculated for performing closed-loop controlling; and the calculated difference is used as the outputting value of the constant-voltage floating charging controller through adjustment by an adjustor. According to the energy storage converter and the control method thereof, floating charging can be realized without a complicated hardware device, so that when charging is performed in a voltage which is next to the upper-limit voltage of a battery, floating charging is performed on the battery in a low current, thereby performing a relatively high protective function on the battery, realizing an effective control method and obtaining relatively high practical engineering value.