基于模耦合理论，从长周期光纤光栅在外加轴向应变或环境温度变化时可能出现的弹性形变、弹光效应、热光效应、热膨胀效应及波导效应入手，推导了描述其轴向应变和温度灵敏度的一般性公式.利用数值方法研究了光栅周期、耦合模式的阶次、弹光系数及热光系数对灵敏度的影响.结果表明：在相同条件下，增大光栅周期将是提高灵敏度的有效手段之一；低次模较高次模的耦合具有更高的灵敏度；包层与芯区的弹光系数(热光系数)相等时，波长漂移量很小且与谐振波长值有简单的正比关系.

Based on mode coupling theory,and considering the physics effect that can be resulted from strain or temperature which affected on long-period fiber grating,such as elastic distortion,strain-optic effect,thermal expansion,thermo-optic effect et al.,the general formula of strain and temperature sensitivities of it were obtained.Computer was used to simulate the relation of sensitivities with the period of LPFG,the order of mode,elastic-optic coefficient and thermo-optic coefficient.The results show that increasing the period of grating or utilizing coupling of the lower order mode will obtain higher sensitivities,and when elastic-optic coefficient(thermo-optic coefficient) of the cladding and core equals,the wavelength shift is very small and in simple direct proportion to resonance wavelength.It will provide some sort of guidance for practical application of sensor based on LPFG.