In order to study the effect of doublevariable coupling upon the fluctuating characteristics of unsaturated rock and soil, the mechanical properties of solid, liquid and gas materials and their relationships with the skeleton were assumed to be mutually decoupled. Based on the engineering mechanics of porous media under small strain condition, the fluctuating control equations for unsaturated porous rock and soil were established by using the Bishop’s average stress and modified suction as the doublestressvariable of skeleton and using the skeleton strain and saturation as the double strainvariables of skeleton. According to the consistency among various kinds of doublevariable linear elastic constitutive models, the functional relationships between the parameters of fluctuating equations and the conventional laboratory geotechnical parameters of unsaturated soil were established. The stiffness matrix for the new fluctuating equations is symmetrical, so that they meet the reciprocity law of elasticity mechanics. The formulas for the velocity calculation of three compressional waves and one shear wave in unsaturated media were established by using the new fluctuating equations. The numerical analysis results show that the doublevariable coupling has no effect upon the shear wave velocity, and little effects upon P2 wave velocity and P3 wave velocity which can be ignored. When the saturation degree is small, P1 wave velocity is obviously influenced by the doublevariable coupling, furthermore the higher the coupling effect is, the more obvious the influence on P1 wave velocity is. However, the influence degree decreases rapidly with the increase of saturation.