Ni target sputtered by CH4 and Ar was used to deposit Ni/a-C:H composite films and thus improve its mechanical, field-emission and tribological properties. The results showed that the composite film exhibited graphite-like C structure with nanocrystal Ni dispersed in it and no bond formed between them. Ni crystals changed from (200) to (111) planes with increasing Ni content, accompanied with increasing surface roughness. Furthermore, the content of sp2C, hardness, maximum current density and frictional coefficient of the film increased firstly and then decreased. Especially, the proper content of sp2C/sp3C and lower surface roughness kept the A2 film (Ni: 14.7 at.%) better field emission performance and higher hardness, and herein better resistance to elastic failure strain and plastic deformation.