Abstract Effusion cooling is the next step in gas turbine blade cooling to get the higher turbine inlet temperature, but the interaction between the front jet flow and the rear jet flow still need to be studied. In this paper, the effect of row number and blowing ratio are studied experimentally by PSP and numerically by RANS. One to five rows of staggered cooling holes were investigated with blowing ratio 0.5, 1.0 and 1.5. It is found that the income boundary layer helps the rear rows penetrate deeper to the main flow at low blowing ratio M = 0.5, the cooling performance become worse for single row. The performance at high blowing ratio M = 1.5 for row 3–5 is nearly not effected by income boundary layer due to blowing off. Finally, a corrected equation based on Sellers superposition method for full coverage film cooling is realized, which could explain the “fully developed level” and improve the accuracy of prediction of full coverage film cooling.