Abstract: The Iaser cell configuration and gas compositions used in reactor pumped ³He-Ar-Xe lasing experiments are presented.The thermal neutron flux of CFBR-Ⅱ reactor, surrounded by high-density polyethylene to moderate the pulse of fastueutrons,is 6×10¹⁴n/cm²·s. According to the structure of polyethylene,the gas compositions is ³He:Ar:Xe=34.7: 34.7: 0.267, 6oomm×Φ34mm(KPa)and the laser cell is Φ 34mm×600mm.The output power is of the level of milliwatts in the first lasing test of reactor pumped ³He-Ar-Xe(λ=1.73μm).