The blue substance had been discovered on wooden artifacts from the Daijiayuan site in Huosan county, Anhui province. It was studied by energy dispersive X-ray fluorescence analysis and ferricyanide qualitative analysis. The results showed that the blue substance is ferrous compound whose formation is associated with the microbe in wood. Besides, the blue substance is covered by yellow one which is proven to be ferric compound by adding the ferricyanide and hydrochloric acid into liquor of ferrous compound.