[Background] In Northeast China, a major maize (Zea mays L.) production region, maize yield is limited severely by insufficient soil potassium supply. Potassium-solubilizing bacteria can mobilize insoluble soil potassium, improve soil potassium availability, and promote maize growth. [Objective] To identify efficient potassium-solubilizing bacteria from maize rhizosphere in black soil, verify their growth-promoting effects under potassium-deficient field condition, so as to provide elite bacteria resource for producing microbial potassium fertilizers adapted to the local environment. [Methods] The bacteria isolated from maize rhizosphere were screened on potassium-solubilizing medium. The taxonomy of the selected potassium-solubilizing bacteria was identified by 16S rRNA gene sequencing. The ecological adaptability (acid and alkali resistance, salt resistance, drought tolerance and pesticide resistance) of the selected bacteria were determined by culturing them on diverse physiological and biochemical mediums. A two-year field inoculation experiment was conducted to verify their effects on maize growth and yield under the condition of potassium deficiency. [Results] Three efficient potassium-solubilizing bacteria, MZ4, KM1 and KM2, were selected. MZ4 and KM2 were identified as Bacillus sp., and KM1 was identified as Brevibacilluse sp.. All the three strains can tolerate drought stress, acid and alkali stress, pesticide (imidacloprid), fungicide (azoxystrobin), and salt stress to a certain degree. In the field without potassium application, the inoculation of MZ4, KM1 and KM2 increased plant height, shoot biomass, leaf area index and chlorophyll content of maize at the jointing and flowering stages. Inoculation with MZ4 and KM2 significantly promoted grain yield by 9.65%?11.50%. [Conclusion] The efficient potassium-solubilizing bacteria which adapt to the black soil in Northeast China were identified. These bacteria can be used as elite germplasm resource for producing microbial potassium fertilizer and analyzing the mechanism underlying efficient potassium solubilization by microorganism.