With increasing X on Ca1-xSrxF2mixed crystals doped with Eu2+(4f65d) ions, the absorption peak shifted linearly to that of SrF2:Eu, while the luminescence one moved parabolically with a minimum at around x=0.5. The linewidth broadened nearly twice as large as that of CaF2in the vicinity of x=0.5 and subsequently renarrowed for x > 0.5. The temperature dependences of the luminescence intensity and life time revealed that the nonradiative activation energy has a minimum of 0.40 eV around x=0.5. From the calculated result of the lineshape, these non-linear behaviors against x were explained by adjusting the electron-phonon coupling strength.