Study is carried out on the low head axial flow turbine (AFT) with aim to utilize the available head efficiently. This focuses on influence of fillet radius at the trailing edge of the runner blade, and the stimulations were carried out for various loads under a constant low head condition. Different models were created in SOLIDWORKS with different fillet radii, i.e. 0 mm, 2 mm, 4 mm, 6 mm, and 8 mm, and stimulated in Ansys Fluent. The results are presented in the form of obtained efficiency ( \(\eta\) ) for corresponding fillet radius (Rtu) and rotor velocity plotted against their equivalent non-dimensional terms of Fillet Radius Ratio (FRR) for different Tip Speed Ratio (TSR). The results indicate that for the given head 0 mm, fillet is the most efficient with maximum efficiency of 56.63% and its performance decreases slowly with fillet radius with efficiency of 55.77% at fillet radius 8 mm.