Due to the high level penetration of several types of distributed energy source, storage system needs to be added in modern power system to suppress power flow fluctuation. In order to realize high efficiency bidirectional power conversion under the circumstance of wide input and output voltage range in energy storage system, a bidirectional buck-boost DC/DC converter based on multi-mode control is studied in this paper. When the input voltage exceeds the output voltage above a certain threshold, valley current mode control is employed and the converter operates as buck region. When the output voltage exceeds the input voltage above a certain threshold, peak current mode control is used and the converter operates as boost region. Furthermore, when the intput voltage is similar to the output voltage, phase-shift mode control is adopted to obtain seamless transition and the converter operates in a manner of buck and boost combination. In order to realize high accurary output and fast dynamics, Type II compensator is employed. By the approach of small portion overlaping between Buck region and Boost region, the discontinuity happened at region transition in traditional Buck-Boost converter is eliminated. 97.5% peak efficiency is achieved in the 1 kW hardware prototype and the transition between Buck region and Boost region is smooth.