The quaternary ZrCrAIN nanocomposite thin films are synthesized by Closed-Field Unbalanced Magnetron Sputtering (CFUBMS). Microstructure and mechanical properties of ZrCrAIN nanocomposite thin films are studied. Grain refinement of ZrCrAIN nanocomposite thin film is occurred by controlling $N_{2}$ partial pressure. Maximum hardness value according to the various $N_{2}$ partial pressures is obtained at 45 GPa. It is also conformed that critical value of the grain size (d) needs to achieve the maximum hardness.