As the next-generation gas turbine efficiency increases, it is required to develop an improved turbine cooling technology to gradually increase the inlet temperature of turbine from 1400 °C to 1600 °C. For this purpose, various studies have been conducted to enhance the external film cooling and the internal cooling performance. This paper proposes the numerical conjugate heat transfer model that is strictly validated with experiment data in order to investigate the heat transfer characteristics of micro-effusion cooling on a flat plate. First, the development of thermal and velocity boundary layer on the flat plate was simulated and analyzed in three kinds of cooling hole sizes. The smaller cooling hole diameter of 0.5 mm maintains a more stable boundary layer along to flow direction than the conventional larger hole size. The second is to compare and evaluate the cooling effectiveness of micro-effusion cooling in two types of cooling hole arrangements, such as aligned and staggered. The staggered array of cooling hole shows the more improved cooling effectiveness by about 350 % from 0.18 to 0.63 than aligned one by 270 % from 0.18 to 0.50 in micro-effusion cooling.