Abstract: Closed circulation is an important way to achieve miniaturization and practicability of high-power pulsed HF lasers. To obtain stable output energy of closed circulation pulsed HF laser, the characteristics of the closed circulation HF laser is studied, and the numerical model of the laser duct is established. Based on the ANSYS application software , the flow rate distribution of the gas medium inside the gain region is analyzed. To acquire better distribution uniformity, different structures of the injection section and transmit section are developed, and corresponding flow fields are simulated and analyzed. A circulation duct with improved distribution uniformity is designed, and the flow rate distribution of the gain region is measured. The results of the experiment and the simulation are consistent.