The laser-induced plasma plays an important role in the trace element analysis. The properties of plasma are dependent on the kinds and pressure of buffer gas. With He, Ar, N2, Air as buffer gases respectively, the time-resolved emission spectra of laser induced Al plasmas at different pressure are measured. The electron density and electron temperature of Nd∶YAG laser-induced Al plasma are calculated by the measured relative emission-line intensity and Stark broadening. The dependence of electron density on the time delay, kinds and pressure of the buffer gas are studied. The time evolution property of the electron temperature is also obtained. The experimental results show that the electron density and the electron temperature in laser induced Al plasmas are the order of 1017 cm-3 and 10000 K respectively. They are both decayed rapidly with the time delay from the laser pulse off and then changed slowly after 4 μs. Among several of buffer gases, the electron density is the largest in Ar gas.