Abstract: Reviewed in the article is the operation situation of the piercer plug bar carriage of the Φ177 mm PQF pipe mills.Accordingly,the original design and maintenance defects that restraint normal operation of the said carriage system are identified, including wear of the tip bearing boring which causes high failure rate of the bearing itself,mounting/dismounting of the axel sleeve which causes reduction of the surface finishing,and frequent wear of the gasket ring,over-standard wear of the lower sliding plate which reduces the service lives of both the wheel and axel of the carriage;over-standard wear of both the front and rear sliding plates which leads to serious vibration of the carriage,and in turn quickens damage of the equipment;frequent breaking of the cooling water piping which causes poor cooling of the plug, and high failure rate of the carriage wheel bearing and so on.Addressing the above mentioned defects,modification actions are determined such as measuring dimensions of the tip bearing boring,and replacing the axel sleeve when dismantling the carriage,periodically measuring the dimensions of the front and rear sliding plates of the carriage to ensure that the wear is within the permissible range,modifying the cooling water piping structure,and increasing the welding strength thereof,selecting new type of the carriage wheel bearing,and periodically checking the oil level and the grease condition,etc.