The main objective of this paper is to find out the boiler efficiency calculation and method to improvement. The thermal industry is known as a major source of conventional energy in India. In the thermal power plant where chemical energy of the coal is converted into electricity. It is most demanding industry now days because of high energy demand. Boiler is the most important part for plant. Running the plant with maximum result we need high boiler efficiency. Calculating boiler efficiency as one of the most important types of performance measurement in any power plant. For calculation of Boiler efficiency basically we use Direct and Indirect method. It is a measure of how effectively chemical energy in fuel is converted into heat energy in steam going to the turbine. Finding boiler efficiency from this method from this method use for boiler efficiency, the data is collected from different department in plant like, Boiler Efficiency Department. Many researchers are find out the boiler efficiency of different plant and carried out their research for improvement of boiler efficiency. This review paper helpful to calculate the boiler efficiency and find out the different types of losses occurs in boiler. We also find that boiler efficiency is always somehow increase by implementing this method and useful for further research.