The time- and space-resolved optical emission spectra (OES) of Si plasma produced by femtosecond laser pulse with center wavelength of 800 nm and pulse width of 100 fs in air were investigated. The results show that the OES mainly consist of continuous spectrum at the early stage of plasma expansion (within the first 50 ns), then the continuous spectrum weakens gradually while the line spectrum becomes dominating. The existence time of ion spectra is shorter than that of atomic spectra in the process of plume expansion. The wavelength red-shift, which has a second order exponential decay with delay time, has been found by the time-resolved emission spectroscopy. Finally, the spatiotemporal evolution of OES intensity are presented.