【Objective】 It is very important to study how soil K-solubilizing bacteria (KSB) vary and its driving factors in the red soil of South China under long-term fertilization, so as to lay down a certain theoretical basis for management of soil potassium (K) resources and rational application of K fertilizer in the region. 【Method】 Based on a long-term fertilization field experiment in red soil that started in 1986, which was designed to have four treatments, that is CK (no-fertilization), NP (nitrogen and phosphorus fertilizers applied), NPK (nitrogen, phosphorus and potassium fertilizers applied), NPKM (NPK fertilizers plus organic manure). Soil samples were collected from the rhizosphere of the maize plants in the plots of the treatments during their florescence for analysis of strains of K-dissolving bacteria and their K-dissolving abilities and organic acids and hormones contents, and for exploration of key factors affecting KSB in upland red soils in relation to properties of the maize root system and physico-chemical properties of the rhizosphere soils. 【Result】Results show that Treatments NP, NPK and NPKM were significantly higher than CK in root length, root surface area and root volume, and so in content of soil organic matter, non-exchangeable K and exchangeable K. Treatment NPKM was the most significant in the effect and 112.3%, 174.4%, 32.43% and 291.5% higher than Treatment NPK in root length, root surface area, root diameter and root volume, respectively; and 0.67 unit, 29.50%, 19.34% and 53.89% higher in pH and content of soil organic matter, Non-exchangeable and exchangeable K, respectively, in rhizosphere soil. KSBs were found in the rhizosphere soils of all the treatments. The KSBs in CK and Treatment NP were of Paenibacillus, while those in Treatments NPK and NPKM were of Cellulosimicrobium. Compared with CK, Treatment NP, NPK and NPKM was 162.4%, 139.0% and 105.6%, respectively, higher in K-dissolving efficiency, showing obviously that Treatment NP was the highest. Moreover, analysis with the the partial least squares path model shows that root and fertilization are that two factors that regulate simultaneously KSB K-dissolving efficiency. Furthermore, redundancy analysis shows that soil KSB characteristics are closely and positively related to root length and root surface area (P<0.05). 【Conclusion】 In the upland red soil, long-term fertilization can not only affect development of the maize root system and physico-chemical properties of the rhizosphere soil, but also alter soil KSB communities and their K-dissolving abilities. Within the root system, root length and root surface area are the two key factors regulating KSB in the rhizosphere soil of maize.