The divergence of spontaneous radiation of fluorescent molecules and low radiation efficiency limit the capture of optical signals in single-molecule fluorescence sensing, and dielectric nanocylinders can effectively improve the directional luminescence intensity of fluorescent molecules. By the finite difference time domain (FDTD) method, it is theoretically studied that the oscillation direction of fluorescent molecules, the distance between the fluorescent molecules and nanocylinders, the refractive index of nanocylinders and the diameter of nanocylinders influence the directional luminescence enhancement. The results show that when the refractive index of the nanocylinder is 1.7, the oscillation direction of the fluorescent molecule is along axial direction of the cylinder, the nanocylinder has a larger diameter and the distance of the fluorescent molecule from the nanocylinder is smaller, the fluorescence directional enhancement effect is better. When the diameter of the nanocylinder is 1 μm and the fluorescent molecule is 10 nm from the nanocylinder, the fluorescence directional enhancement is about 10 times and the directional emission angle is about 16.1°.