Abstract: Coking in coal-fired boilers will cause great harm to the safety and economy of boiler operation.Therefore,it is important to analyze the factors affecting coking of coal-fired boilers and effectively prevent coking in coal-fired boiler. In practical application,different preventive measures can be taken for different factors affecting coking of coal-fired boiler.It is found that the melting temperature of coal ash,particle size of coal,combustion atmosphere of boilers,primary and secondary air force field,thermal loads of boiler section and boilers are the factors that affect the coking of coal-fired boilers. In order to solve the problem of large area combustion coking in precombustion chamber,furnace and convection heating surface in a specific pulverized coal boiler,based on combustion coking mechanism of coalfired boilers,the measures of by adjusting combustion atmosphere,increasing secondary air rigidity,reducing the pulverized coal particle size,replacing the pulverized coal were taken to analyze coking phenomenon under different conditions. The conclusion is that the types of coal and the particle size are the factors affecting the combustion coking of this specific pulverized coal boiler.The micro morphology and element composition of the coking block as well as the composition of different coals were analyzed by SEM-EDS,the coal quality and ash composition between the coal powder currently used in the on-site sampling boiler and Sunjiacha coal powder were compared and analyzed,and the slagging discrimination index was calculated according to the ash composition.The melting temperature of coal ash used in the boiler is relatively low.The softening temperature Ts is 1 170 ℃,less than 1 200 ℃ .It is called fusible coal and easy to slag and belongs to a typical kind of easily coking coal.The calculation results of slagging discrimination index show that 4 indexes are evaluated as " serious",1 index is evaluated as " medium",meaning high slagging tendency.In general,the change of coal type and the low melting temperature of the coal are the essential factors affecting the combustion coking of the boiler.To further solve practical problems,the acid-base equilibrium of coal ash was destroyed to increase the melting temperature and the particle size was refined by the following methods,5%quartz was blended into the coal to increase the content of Si O2 and thus increase the melting temperature of the coal to 1 280 ℃,and the temperature would be increased by 110 ℃ .The frequency of pulverized coal mill was turned up from 19 Hz to 22 Hz to increase the sieving rate of pulverized coal particle size( 200 mesh) from 70% to 85%.Eventually,the boiler ran smoothly and the coking condition is improved significantly.Overall,the combustion adjustment measures achieve good results and relevant experience are available for reference.