Abstract: ［Abstract］Objective To evaluate changes in cerebral blood flow before and after cranioplasty by 256-slice Spiral CT perfusion imaging， and evaluate the effect of cranioplasty on the cerebral blood flow in patients with skull defect. Methods 256-slice spiral CT scan was performed in 20 cases with early cranioplasty surgery， CTP check time points were 1 to 2 days before and 10 to 14 days after cranioplasty surgery. We recorded the the CBF and CBV of the cortex， basal ganglia， and thalamus and other parts， MTT on rCBV， parameter values rCBF， MTT and 1TrP etc. and analyzed and compared. （RCBF， rCBV， MTT and TTP） Results The CBF of cortex after cranioplasty at injured side had statistically significant increase（P＜0.05）. The CBF of cortex，basic nuclei，thalamus on contrateral had no statistically significant difference． The cerebral blood flow on both sides of the basal ganglia and the thalamus was increased after surgery， but there was no significant difference between before and after surgery（P＞0.05） Conclusion　Cranioplasty can significantly improve the ipsilateral cortex cerebral blood flow， and CT brain perfusion can accurately assess changes in brain tissue blood flow before and after cranioplasty.