This work proposes a two-dimensional porous lithium niobate grating-coupled birefringent Bloch surface wave (BSW) sensor. Based on the nonlinear characteristics and birefringence of lithium niobate, the theoretical study investigates the impact of two refractive index excitation schemes, ne and no, on the tunability of the BSW. First, we construct a four-period TiO2/MgF2 stacked distributed Bragg reflector (DBR) and deposit a layer of two-dimensional porous lithium niobate grating on the top of the DBR to achieve wave vector coupling. This successfully excites the BSW at the interface of the sensor and the sensing medium. Second, by rotating the incident light, we switch between the ne and no excitation schemes of lithium niobate, introducing the concept of azimuthal detection to explore the tunability of lithium niobate BSW sensors. The results show that the azimuthal angle variation of BSW resonance peaks for both refractive index excitation schemes is approximately 5 deg. Finally, we perform numerical analysis on the sensor performance for both excitation schemes. The results demonstrate that the sensitivity and quality factor of BSW sensors excited along ne and no refractive indices reach 3782 °/RIU (12400 /RIU) and 2967 °/RIU (6682.5 /RIU), respectively. This confirms the great potential of lithium niobate as a nonlinear tunable material in the field of BSW sensors.