Diamond-like carbon (DLC) film prepared by pulsed laser deposition is one of excellent means for antireflective and protective films of infrared (IR) window. DLC film on silicon is prepared by 248 nm nanosecond laser, and influence of pulse energy on optics performance, mechanical hardness and residual stress of DLC film are studied. According as experiments, IR transmission and surface hardness of the films both increase along with increasing of laser pulse energy, which indicates that high energy is propitious to prepare protective DLC film for IR window. However, residual stress in DLC film is also increased to reduce the adhesion strength of the film on substrate. This result supplies the practice base to the study on DLC film prepared by nanosecond pulse laser deposition.