Soil phosphorus (P) is an essential nutrient for plant growth and a major limiting element for productivity in subtropical forests. Currently, there is no unified conclusion on the change of soil P fractions and P availability at different elevations, primarily because the response of P fractions and availability at different elevational gradients caused by the change in vegetation types is complex. This study analyzed Pinus taiwanensis forest in Wuyi Mountain with different elevational gradients to explore the transformation and availability of soil P fractions and its influencing factors. We examined the soil environmental factors, physicochemical properties, microbial biomass (SMB), acidic phosphomonoesterase (ACP), phosphodiesterase (PD) levels, and soil P fractions. The results showed that the content of soluble P increased significantly with the decrease of elevation, while the content of labile P, moderately labile P, occluded P, and total phosphorus noticeably decreased. Redundancy analysis showed that microbial biomass phosphorus (MBP) and nitrogen (MBN) were the determining factors affecting soil P fractions. Our findings suggested that with a decrease in elevation, soil microorganisms promoted the transformation of P fractions. This occurred mainly through their energy allocation strategy, which increased the activities of ACP and PD and decreased SMB content; soil microorganisms in turn accelerates the mineralization of non-labile P, thereby increasing the content of soluble P that meets microbial demand. As a result, due to the relative lack of P element in lower altitudes, microorganism can obtain more available P through energy allocation strategy, which could help increase the supply of soil soluble P in Pinus taiwanensis forest of Wuyi Mountain. However, it may lead to an insufficient P reserve pool over the long term, which may have an adverse effect on the sustainable supply of soil P.