The time and spatial-resolved emission spectrum of Co atom 389.408 nm spectra line in laser induced Co plasma was measured. The electron density of plasmas was calculated from the measured intensity and Stark broadening of emission spectral line. The time and spatial evolution properties of the electron density were finally discussed. The measured results show that the plasma electron density is varied from 0.02×1017 to 0.73×1017 cm-3 when the time delay is in the range from 100 to 1000 ns. It is also concluded that the plasma electron density is varied from 0.3×1017cm-3 to 0.8×1017 cm-3 along the direction of the laser beam when the distance from target surface is in the range from 0 to 1.8 mm. The distribution of the plasma electron density along the laser beam has well symmetry.