Such problems as flameout and serious slagging frequently occurred in a 170 t/h tangentially fired boiler burning inferior coals and with low load.Thus,cold tests were carried out to comprehensively investigate the performance of each air tube and the size and position of the tangential circle.Therefore,the cause and area of slagging in furnace can be determined.Thus,by numerical simulation on combustion,the optimal operation parameters for the boiler burning different coals under various loads conditions can be provided.The actual application showed that,the boiler fed with present coal can be long-term operated stably at 60% load,and its heat efficiency was up to 91%.Moreover,the abnormal flameout no longer occurred,and the slagging was alleviated a lot. Such problems as flameout and serious slagging due occurred a 170 t / h tightened substantially fired boiler burning coals and with low load.Thus, cold tests were carried out to comprehensively investigate the performance of each air tube and the size and position of the tangential the cause and area of ​​slagging in furnace can be determined.Thus, by numerical simulation on combustion, the optimal operation parameters for the boiler burning different coals under various loads conditions can be provided. The actual application showed that, the boiler fed with present coal can be long-term operated stably at 60% load, and its heat efficiency was up to 91%. Moreover, the abnormal flameout no longer occurred, and the slagging was alleviated a lot.