Abstract: In recent years,the development of new energy has put forward higher requirements for the flexible operation of thermal power units. Therefore,it is imminent to thoroughly study the operation mode of the deep peak shaving of the thermal power unit and solve the related technical problems. CFB boiler can realize stable combustion at low load and has the natural advantage of deep peak regulation. Due to the characteristics of small investment,short modification period and good thermo economy,the flexible low pressure( LP) cylinder cutting technology based on steam process reconstruction is an efficient way to achieve deep peak shaving of cogeneration units and realize thermoelectric decoupling. Based on the practical experience of a 350 MWe supercritical CFB boiler cogeneration unit,the follow-up operating problems of LP cylinder cutting technology in CFB boiler unit were analyzed and the corresponding solutions were proposed. During reconstruction,the wide-range control technology to avoid flutter was used for the first time in China. The online monitoring flutter equipment was developed and installed for the first time in the same type of domestic units. Also,the technology of extracting five-stage extraction steam to six-stage extraction steam was used for the first time. Through technical transformation,the key follow-up problems like low pressure cylinder blast under the condition of cylinder cutting,blade erosion and flutter,safe operation of the turbine,air cooled antifreeze,low temperature corrosion of air preheater,fuel system fluctuation and interlock protection fitment were solved by a series of technologies.Compared with the conventional LP cylinder cutting reconstruction,the wide-range cylinder cutting control technology adopted is more flexible and smoother,which eliminates some hazards of the previous rapid cylinder cutting technology. Among them,the reconstruction of the supporting system of CFB boiler provides guarantee for its high fuel flexibility. Based on the low load stable combustion characteristics of CFB boiler,the unit operates safely after the low pressure cylinder cut-off transformation and reaches the NOxultra-low emission standard. Not only is the thermoelectric decoupling achieved,the load regulation range is widened from 60%-94% to 30%-94%,and the heating capacity is increased by 50%,but also the purpose of energy saving and consumption reduction in heating period is achieved and the the ratio of district heating and electricity generation is enhanced especially under low load,which improves the resource utilization and unit thermal economy. Under 40% load conditions,the the ratio of district heating and electricity generation increases from 0.97 to 2.11 and the coal consumption in generation is reduced by 70.49 g/k Wh. Above all,the new flexible LP cutting reconstruction technology proposed in this paper has solved a series of technical problems,achieved a number of technological breakthroughs,accumulated operating experience and made contributions to tapping the great potential of the peak shaving of the cogeneration unit,improving the operational flexibility of thermal power in China and the capacity of the new energy consumption.