A 1.2~3μm band laser film filter was developed on doubleside polished Si substrate using the ion beamassisted thermal evaporation deposition technique. The film sample was designed combination of long wave pass filter film and antireflection film. The high and low refractive index materials are ZnS and MgF2 monolayer films, respectively. Considering the spectral properties and intensity distribution of electric field, the 1.064 μm high reflection and 1.2~3 μm antireflection long wave pass filter were designed by a TFCale software. The longpass film system structure and the antireflection film structure are G|4H2L1.5H2L2H1.5L2H4L|A and G|3.5H3.5L|A, respectively. The results show that the peak transmissivity can approach 98.48%, the average transmissivity is 92.35% at the wavelength of 1.2~3 μm, and the transmissivity is 5.09% at the 1.064μm band. By ion beam and annealing treatment, It was found that the appropriate processing parameters contributed to the improvement of the laser induced damage threshold, when the annealing temperature is 250℃, the laser induced damage threshold is 6.3 J/cm2. This research provides application value for the design and preparation of near infrared thin film filters.