Microgrid can operate in either grid-connected mode or island mode. When in island mode, the ability of master micro-source to regulate voltage and frequency has a significant impact on the stable operation of microgrid. This paper is based on the built PV-Diesel-BESS microgrid with storage batteries as the master micro-source. Three groups of comparative experiments are conducted, respectively in different state of charge, different load disturbance and whether connecting the diesel into the microgrid. Relevant waveforms are recorded using three-phase power quality analyzer to analyze operating characteristics of microgrid under different experimental conditions. Experimental results show that the state of charge and load disturbance have important effects on stable operation of microgrid in island mode. The diesel will occupy the leading role in regulating voltage and frequency when connected into the microgrid. The capacity of energy batteries need to be optimized. According to the experimental results, battery capacity is optimized to ensure the leading role of energy batteries.