In order to explore the matching rule of cotton root growth，morphological characteristics and nutrient efficiency with phosphate fertilizer drip application，a pot experiment was conducted with ‘Xinluzao 63’ cotton as the research object. Five treatments were set up，including no phosphate fertilizer(CK)，basal application of ammonium phosphate(PB)，drip application of ammonium phosphate(PD)，drip application of ammonium phosphate+polyglutamic acid(PDS1)，and drip application of ammonium phosphate+microbial agent(PDS2). The effects of phosphate application methods on root morphological characteristics and phosphate effectiveness of cotton were analyzed and compared. The results showed that，compared with CK treatment，the root length and root surface area of medium root(mean diameter 0.2-0.4 mm)and coarse root(mean diameter greater than 0.4 mm)were reduced by phosphorus application，while those of fine root(mean diameter less than 0.2 mm)were increased. At seedling stage，the total root length of PB treatment was significantly increased by 26.28%，compared with CK treatment. Compared with PB treatment，the root volume of PD treatment was significantly increased by 43.07%. Under the drip application conditions，the root parameters showed a pattern of PDS1>PDS2>PD. At bud stage，compared with CK treatment，total root length，root surface area and root volume of PB treatment were significantly increased by 31.14%，62.55% and 176.66%，respectively. Compared with PD treatment，the total root length，root surface area and root volume of PDS1 treatment were significantly increased by 26.05%，37.76% and 16.98%，respectively. In flowering and bud stage，compared with CK treament，total root length，root surface area，root volume and root diameter of cotton treated with PB treatment increased by 5.61%，10.04%，39.09% and 10.57%，respectively. Compared with PB treatment，the total root length of PDS1 treatment was significantly increased by 20.31%，and the root surface area of PDS2 treatment was significantly increased by 34.10%. Under the conditions of drop application，the total root length and root surface area of PDS2 treatment were significantly increased by 18.49% and 33.33%，respectively，compared with PD treatment. Compared with CK treatment，PDS1 and PDS2 treatments significantly increased the fine root length and root surface area of cotton in the later stages of crop growth(bud stage and bud stage). The available phosphorus content in the soil of each phosphorus application treatment was significantly higher than that of the CK treatment during the seedling and bud stages，and overall showed an increasing trend with the progression of the growth period. The utilization rate of phosphorus fertilizer in cotton during the seedling and bud stages was significantly positively correlated with total root length，while the utilization rate of phosphorus fertilizer during the flowering and bud stages was significantly positively correlated with total root length，root surface area，and root volume. Overall，the drip application of phosphorus fertilizer combined with microbial agents could promote the growth of cotton roots，thereby promoting phosphorus absorption and utilization.