Abstract: An improved type of pumping lamp condenser and cooling cavity for YAG laser is designed and described, where a quartz glass tube is inserted between the elliptically cylindrical mirror cavity and the pumping lamp and laser rod,and the cooling water is flowed through the tube with lamp and rod immersed in it. This kind of modified configuration has advantage over current cavities. Its cooling efficiency is higher than that of lamp and rod respective cooling structure, and its gold-coated mirror protection is better than that of the full cavity cooling structure.In the current structure, the pumping lamp and the laser rod are set in the position of two focal axes of the elliptically cylindrical mirror, which are conjugate, without any spherical aberration, according to the geometry. However, this condition is not properly satisfied in the improved configuration and the conjugate should be consulted by computer manipulation. Therefore the mathematical formulae for ray tracing in this special system are derived and the evaluation criterion is determined. The refraction indices of water and quartz glass are calculated for wavelength and respectively, which are emitted from the pumping lamp and absorbed by YAG laser rod. The ray tracing program is compiled and the results are investigated. It is concluded that the pumping lamp and the laser rod should be shifted forward to each other from the foci of that mirror and the optimum conjugate can be found so that the concentric beam from the lamp is nearly concentrically converged to the rod.