Time-resolved emission spectrum from laser-produced plasmas by 1.06μm, 10ns laser pulse's irradiation on silicon target surface in air at a flux of 9.3×109 W/cm2 isrecorded and analyzed between 200 and 880 nm. The ignition time of the plasma isestimated. The expansion velocity of Si atoms in the plasma is measured.A mechanism ofthe N+ ion formation in the plasma is proposed to explain the appearance of N+ ions observedin the plasma. It was found by means of measuring the variation of the FWHM of Plasma's the emission line at different delay time that the electron density in the plasma decreases approximatively as an exponential of exp(-t1/2).