The effect of two symmetrically distributed fin-shaped strips on hydrodynamic forces and flow structures of a circular cylinder is numerically investigated at low Reynolds numbers of 60–180. The angular position (θ), defined as the angle between the starting point of the strips and the front stagnation point of the cylinder, is varied from 30° to 90°. It is observed that the boundary layer separation is tripped by the strips, altering the pressure distribution and forming a recirculation region behind the strips. As a result, the drag and lift coefficients are increased significantly. At θ = 30° and 40°, the boundary layer reattaches on the cylinder surface after the first separation from the strip tip, followed by the second separation. However, when θ is larger than 50°, the separation point is fixed at the sharp corner of the strips. Compared to θ ≤ 40° and θ ≥ 70°, shorter wake formation length and larger wake width are observed at θ = 50–60°, resulting in the larger drag force and faster vortex shedding. The strips placed at θ = 40–70° have more contribution to the alteration of flow structure than those positioned at θ = 30° or 80°–90°. At Re = 180, placing the fin-shaped strips at 60° maximally increases the lift and drag coefficients by 40.03% and 16.98%, respectively, in comparison with the bare cylinder.