Objective To investigate the effect of simple cranioplasty on hydrocephalus after decompressive craniectomy.Methods A two-way cohort study was performed for 112 patients who underwent cranioplasty in Department of Neurosurgery， The Second Affiliated Hospital of University of South China， from September 2017 to September 2020， and according to the presence or absence of hydrocephalus before surgery， the patients were divided into observation group （40 patients with hydrocephalus） and control group （72 patients without hydrocephalus）. The two groups were compared in terms of preoperative condition， postoperative complications， ventricular changes， Barthel index， and Mini-Mental State Examination （MMSE） score.Results Compared with the control group， the observation group had significantly higher age， defect area， and number of patients with aneurysm （P <0.05）， while there was no significant difference in the incidence rate of complications between the two groups （P >0.05）. The patients were followed up at ≥3 months after surgery， and compared with the control group， the observation group had a significantly higher proportion of patients with a reduction in the ventricle after surgery， but such reduction did not help the patients recover from hydrocephalus （P <0.05）. Both groups had significant increases in Barthel and MMSE scores （P <0.05）， but there was no significant difference in the improvement rate of these scores between the two groups （P >0.05）. The correlation analysis showed that there was no significant correlation between postoperative score improvement and ventricular changes in patients with hydrocephalus （P >0.05）.Conclusions Simple cranioplasty is safe in patients with hydrocephalus after decompressive craniectomy. Although ventricular enlargement cannot return to normal， most patients with hydrocephalus may achieve the improvements in neurological function and quality of life.