The ring resonator can be used for high precision and high sensitivity sensing. In this paper, the ring resonator is combined with cantilever pressure sensor. The expression of sensitivity of this pressure sensor is derived, the sensitivity will vary with the applied pressure. When the pressure is 1 kPa, the sensitivity is 71.73 pm/kPa. Lithium niobate on insulator (LNOI) which has low loss is used to design ring resonator to obtain a pressure sensor with high Q. It can improve the accuracy of pressure measurement. The effects of critical coupling and non critical coupling, waveguide loss and the perimeter of the ring waveguide on Q factor are discussed and analysed by Matlab. The results show that the most important factor is the waveguide loss. The increasing of the perimeter of the ring waveguide will not increase the Q factor directly, but will reduce the loss and increase the Q factor indirectly. The results show that when the radius of the ring waveguide is 80 μm and the waveguide loss is 0.6322 m^-1, Q factor can reach 5.7×10⁶.