Abstract: In order to screen the biochar (BC) that can provide suitable living space for Raoultella ornithinolytica (Ro), a series of biochar carriers were obtained by maize straw (MSC), wheat straw (WSC) and rice husk (RHC) under the oxygen limited conditions by 300 ℃, 500 ℃ and 700 ℃, respectively. The effects of BC, Ro and Ro-BC on the availability of P and K in purplish soil were explored by lab-incubation with the carriers by MTT colorimetric method and ATR-FTIR method. The results showed that MSC500 was the best carrier for Ro with an obvious stretching vibration peak by the functional groups of C = C and —OH, and the stretching vibration peak of C—O—C bond was widened and deepened as well. Moreover, the application of Ro and Ro-BC significantly improved the bacteria quantity and the availability of P and K in different purplish soils. Compared with the control, Ro-BC had the best effect on the bacteria quantity and Olsen-P, which increased by 61.1% ~ 276.3% and 22.8% ~ 82.5%, respectively. However, the Olsen-P was decreased after 168h incubated. For available K, the application of Ro had the best effect on acid purplish soil (increasing by 46.3%), while the application of Ro-BC had the best effect on the neutral and calcareous purplish soils (increasing by 29.8 % and 71.23 %, respectively). In general, suitable immobilized materials for different Ro could increase the activities of Ro strains, improving soil microenvironment to promote the availability of soil P and K.