The invention relates to a device for improving stability of deep ultraviolet (DUV) lasers. The device comprises a DUV nonlinear frequency-conversion crystal device which is formed by clamping a DUV nonlinear frequency-conversion crystal between two right-angle prisms and closely combining the three through a metal shell, wherein the top surface and the bottom surface of the metal shell are provided with heat-dissipating devices respectively; a layer of heat-conducting media is arranged between the heat-dissipating devices and the metal shell of the nonlinear frequency-conversion crystal device; the metal shell of the DUV nonlinear frequency-conversion crystal device is closely fixed together with the heat-dissipating devices through screws or adhesive; coolers are positioned between the heat-dissipating devices and the metal shell and are in close contact with the two through the heat-conducting media; and the coolers are electrically connected with a temperature control instrument. The device adopts a temperature control technique to control the DUV nonlinear frequency-conversion crystal at a certain set temperature in order to maintain phase matching, thereby effectively solving the problem of the thermal instability of DUV nonlinear frequency-conversion lasers and enabling the DUV nonlinear frequency-conversion lasers to be more practical.