Microring resonators are key components in nowadays photonic integrated circuits. A vertical microring resonator with enhanced tolerance to fabrication misalignments is introduced. Both straight and microring waveguides are with relatively high refractive-index difference between the core and cladding, therefore the vertical microring resonator is compact and confines the power efficiently. Based on coupling mode theory, the coupling coefficient is derived as a function of the coupling layer thickness (d) and the transverse offset (Δ) between the straight and microring waveguides. The analytic solutions are used to confine the range of three-dimensional finite-different time-domain (3D-FDTD) simulations for their efficiency. In addition, the tolerance of d and Δ is studied by taking consideration of actual fabrication technology for the vertical nano-microring resonator. The analytic solutions and simulation results show that when d=30 nm, the vertical microring resonator has a large coupling coefficient even Δ is varied from 130 to 265 nm. It is verified that the vertical nano-microring resonator has enhanced tolerance to fabrication misalignments.