The Hanguang Entrance remains of the Tang Dynasty provides valuable historical,cultural and scientific information.As time goes by,a wide range of biological damage has occurred,and urgent action needed to be taken to rescue the site.After a detailed investigation of biological damage,it was found for the first time that insects and mites can cause severe damage,and that cyanobacteria and fungi are main damage factors.The causes and mechanism of these biological diseases have been analyzed.Prevention and control measures have been investigated.These studies lay a solid foundation for further rescue protection.