TiAlSiN nanocomposite coatings were deposited by modulated pulsed power magnetron sputtering (MPPMS) with the varied peak power from 24.8 to 56.8 kW. The coatings had a typical nc-TiAlN/a-Si3N4 nanocomposite structure. The microstructure of the coatings changed from a columnar structure (Zone I in Thornton's Model) at 24.8 kW and 35.2 kW to a dense glassy-like structure (Zone T) at 44.6 kW and 56.8 kW. With increasing peak power from 24.8 to 56.8 kW, the hardness increased from 23.6 to 31.3 GPa, the H/E* changed from 0.079 to 0.091, elastic recovery (W-e) increased from 50.1% to 57.4%, and compressive macrostress (sigma) changed from - 0.16 to - 1.59 GPa. Fracture toughness (K-IC) of the coatings was measured by the indentation test with a Vickers diamond indenter at the load L of 500 mN and 1000 mN. K-IC increased from 0.96 to 1.77 MPa.m(1/2) with the peak power from 24.8 to 44.6 kW, except for no fracture at the highest peak power of 56.8 kW. The highest hardness, H/E* ratio and elastic recovery of 31.3 GPa, 0.091, 57.4% with the macrostress of -1.59 GPa were obtained at the peak power of 56.8 kW. The enhanced toughness of TiAlSiN nanocomposite coatings was obtained at peak power of 44.6 kW and 56.8 kW, which was attributed to dense structure in the Zone T at high peak power. Effect of the bombarding energy (E-bi) and surface mobility (D) of the incident species on Zone T structure was explained by the electron densities and temperature, and number densities of Ti and Al sputtered species simulated using a global plasma model. The critical parameter of structural transformation from a columnar structure to a dense glassy-like structure is the increase of bombarding energy E and mobility of species D. The flexible and hard TiAlSiN nanocomposite coatings were deposited by MPPMS at higher peak power.