Thermal lens is an important factor limiting the power increase of las er.The thin-disk structure has some advantages in heat dissipation,but the th e rmal lens effect under high power pump is still an unavoidable problem.Based on the heat conduction equation and finite element software,the model of water-c o oling disk laser is constructed.The temperature distribution,end-deformation a nd stress distribution of the whole laser structure are analyzed in detail under the condition of 300W pump power.On this basis,the effect of mechanical stres s on the improvement of crystal thermal lens is analyzed.Compared the analysis results after compensation,when 100N positive pressure is produced in the settl ing plate of heat sink to compensate thermal deformation of the thin-disk cryst a l,the end-deformation of thin-disk crystal is less than uncompensated one.Th e thermal lens effect of Yb:YAG water-cooling laser improved obviously.In additi o n,the thermal lens effect of laser can be improved by properly increasing the p ositive pressure when thin-disk crystal is installed.