Abstract: A number of brick chimneys have served for about 30 years.Due to their performance serious degradation and the relatively low level of construction,the normal safety of the brick chimneys is concerned in subsequent service life.So a damaged brick chimney was studied which had served for 30 years in an industrial building.According to the results of detection and analysis of related items such as actual size,inclination,crack,deformation and other important indexes,the serious ageing and the damage of brick chimney were discovered and cracks were the main diseases.The checking calculation of bearing capacity was done with analysis of ANSYS on the basis of measured data,the conclusions were drawn that bearing capacity was obviously insufficient at the bottom and security surplus was small in the upper part.And further the cause of disease was explained from the theoretical point of view． Reliability of the chimney was evaluated by the reliability factors.In view of existing security problems a reinforcement program of gluing flat steel reinforcement was made.And modal analysis was studied by ANSYS before and after reinforcement,so the difference of mechanical behavior was compared and analyzed.The results showed easy construction and low cost of the reinforcement method.Although the strengthened brick chimney had worked normally for 2 years,each performance was generally satisfactory．