A highly sensitive one-dimensional photonic crystal magnetic and thermal sensor with lithium niobite (LiNbO₃) used as the defect layer is proposed. The rigorous coupled wave analysis theory and the wavelength interrogation method were performed to further investigate the effects of different defect layers and magnetic fluid film structure parameters on the sensitivity and figure of merit (FOM). The results show that the introduction of LiNbO₃ can significantly improve the sensing performance. When LiNbO₃ was introduced as the defect layer, the magnetic field detection sensitivity increased from 0.817 to 1.9133 nm / Oe, whereas the temperature detection sensitivity increased from −0.0724 to 0.304 nm / ° C. Meanwhile, it provides a high FOM value of 8.7099 Oe ^{− 1}. Our work provides a guideline for the future application of LiNbO₃ materials in magnetic and thermal sensors.