【Objective】To study the relationship between bridging septa thickening in the perinephric space and split renal function in acute unilateral upper urinary tract obstruction.【Methods】50 patients with acute unilateral upper urinary tract obstruction by calculus were analyzed retrospectively. According to the images of multi-slice spiral CT （MSCT）scanning，all cases were divided into thickened bridging septa group（n=25）and normal bridging septa group （n=25），The CT values of renal cortical in the plain（CTp）and renal cortical enhancing（CTe）phase were measured， the difference of increasement value（CTe-CTp）and the CT value ratio of the ipsilateral and opposite in renal cortical phase was analyzed by independent sample T test.【Results】The CT increasement value of bridging septa thickening and normal group were（103±30）HU and（128±24）HU respectively，the difference between the two groups was statistically significant（P<0.01）；and CTac/CTuc were 0.81±0.13 and 0.96±0.06 respectively（P<0.01）.【Conclusion】Thickening of bridging septa in the perinephric space with acute unilateral upper urinary tract obstruction will weaken the enhancement of renal cortical，and increased the likelihood of split renal function impairing.