Abstract: The limestone system of DG520/13.7-Ⅱ1 CFB boiler in some power plant has the problem of frequent piping block in operation, which leads to the limestone supply interruption and the variation of sulfur dioxide, or even excessive discharge, which can not satisfy the demands of environmental protection.After the inspection and analysis of blocked pipes, effective measures have been adopted.Such as increasing the pressure of limestone's compressed air, periodic drainage, strict control of the limestone's particle size and humidity, introduction of column limestone distributor, increasing the length of main limestone pipes, shortening the length of branches and improving the operational skills.Finally, the problem of piping block has almost been solved and the operating reliability of limestone system has been enhanced.Meanwhile, the sulfur dioxide emission comes up to the standard.The solution has provided useful reference to the same problem of CFB boiler.