A novel laser gain medium, microsphere array cooled by refractive index-matched coolant, is presented in response to the thermal management of high-power solid-state lasers in this paper. Experiments on microsphere array lasers in circulating state are carried out. The emission spectra and flourescence decay curves are measured. Besides, the stable pulse output energy is achieved and its laser characteristics are studied. The maximum pulse energy of microsphere array laser with diameters of 2 mm and 4 mm are 30.2 mJ and 115.4 mJ, respectively at a repetition rate of 1 Hz, and the corresponding slope efficiencies are 4.6% and 16.2%, respectively. Output energy decreases as pumping frequency increases. Experimental results show that the microsphere array laser has relatively good thermal performance and thermal stability, and can be used in high-power laser systems.