This paper presents our experimental investigation on the characteristics of laser produced silicon plasma column as an X-ray gain medium in which the soft X-ray spontaneous emission amplification is demonstrated succesfully. It is found that the soft X-ray emission from 5A～100A of the plasma under this condition is mainly contributed from the He-like (Si12+) ions to Li-like (Si11+) ions recombination radiation and the Li-like ions n=3-n=2 transition emission and the strongest emissions occur at about 130μm from the target surface, with the corresponding electron density 3×1020 /cm3. The average ratio of the He-like ions to the Li-like ions on the 1S23d level is about 36. The reabsorption of the Si11+1s23d-1s22p transition is also observed of experimentally.