The invention provides an analyzing method of time-varying mesh stiffness of a single roller enveloping worm gear pair and aims to acquire the time-varying mesh stiffness of the single roller enveloping worm gear pair. The method includes: deducing worm tooth bending stiffness, shear stiffness and radial compression stiffness formulas; calculating worm tooth base stiffness; calculating worm gear tooth bending stiffness and shear stiffness; calculating worm gear tooth base stiffness; calculating worm stiffness and worm gear stiffness at a disperse contact point; calculating contact stiffness; performing serial and parallel calculation on the worm stiffness, the worm gear stiffness and the contact stiffness; calculating the time-varying mesh stiffness. The method has the advantages that the time-varying mesh stiffness of the single roller enveloping worm gear pair can be calculated, the worm gear stiffness and the worm stiffness can be further decomposed, the worm tooth bending stiffness, shear stiffness and radial compression stiffness formulas are provided, a calculation model of the number of meshing worm gear teeth in a mesh cycle is provided, and the method is applicable to the dynamic performance analysis and optimization design of the single roller enveloping worm gear pair.