In this work, we achieve a four-fold enhancement in thermo-optic coefficient measurement resolution for KTiOPO4 crystal using a self-stabilized birefringence interferometer integrated with cascaded second-harmonic generation. We observe the tunable interference beating phenomenon by rotating a birefringent crystal versus the temperature of the crystal. Furthermore, the fourth harmonic interference fringes beat 4 times faster than the fundamental wave interference fringes. This beating effect is used to determine the thermo-optic coefficients of the two principal refractive axes with a single measurement. This work provides a feasible, real-time, and robust method for super-resolution measurements based on birefringence interferometry.