Abstract: Objective To study the therapeutic effect of local polylactide acid-glycolic acid copolymer（PLGA）-dexamethasone on traumatic cerebral edema（TCE） in rats under high temperature（HT） and high humidity（HH） environment and its possible mechanism. Methods Twenty-four healthy adult SD rats were randomly divided into local PLGA-dexamethasone group,mannitol group,and control group（8 in each group）.An acute cerebral injury model of mice was established by placing them in an HT（35℃） and HH（RH 85%） environment with the free-falling body method.Rats in mannitol group were given mannitol（2g/kg） immediately after injury through veins and a maintenance dose was added after 6h.Cerebral water content（CWC） was measured with the dry-wet method after 24h.Expression of AQP4 protein and AQP4 mRNA was detected by immunohistochemistry and in situ hybridization,respectively. Results The expression level of AQP4 and CWC was significantly lower in PLGA-dexamethasone group and mannitol group than in control group（P＜0.05）.However,no significant difference was found in expression of AQP4mRNA between the two groups（P＞0.05）. Conclusion Local PLGA-dexamethasone can decrease the incidence of TCE and the expression of AQP4 and AQP4 mRNA by changing the water transportation around TCE.