Measurement of the extent of damage is very important for structural safety assessment and strengthening design of Chinese ancient timber buildings. The present damage index values were surveyed according to the technical code for maintenance and strengthening of ancient timber buildings published in 1992 (GB 50165—92). In order to verify and revise the integrity damage indexes of this code, the integrity and mechanical performance of some mortisetenon joints and timber frames were tested. Then the integrity damage indexes of the post and lintel construction and the column and tie construction in the traditional timber buildings in south China are presented. These damage indexes are analyzed in comparison with the regulations of the previous national code. The results show that 1) the damage indexes of local inclination of these two constructions are much smaller than the test results and, therefore, the previous regulation codes are on the safe side; 2) the damage index of mortisetenon joint connection in the post and lintel construction regulated in the code is slightly smaller than the test results and, therefore, the regulation codes are safe for the buildings; 3) the damage index of mortisetenon joint connection in the column and tie construction regulated in the code is smaller than the test result for the Yanwei mortiseten on joint and, therefore, the regulation of the code is safe; 4) however, the damage index of mortisetenon joint connection of the column and the tie construction regulated in the code is larger than the test result of Tou Mortisetenon Joint and, therefore, the regulation of the code is not safe in this case.