In this study, we analyze the focusing properties of the cylindrical vector beams through a subwavelength grating lens with a negative refractive index and the effects of grating material and geometric parameters on the focusing properties. Here, the equivalent negative refraction can be attributed to the subwavelength grating's diffraction order of -1, and the focusing plane-concave lens can be designed using the equivalent optical path method. Further, we use the finite element method in a cylindrical-symmetric coordinate system to simulate and analyze the effects of different material refractive indices, equivalent negative refractive indices, and predetermined focal lengths on the focusing properties. The results denote that the material refractive index significantly affects the energy efficiency of the focal field, the focus size is minimized by an equivalent negative refractive index of -1, and the short predetermined focal lengths yield small focus sizes. The proportion of longitudinal electric-field components in the focal field is the main factor that determines its lateral size. Therefore, the optimum focusing effect can be obtained by selecting an appropriate negative refractive index of the grating and a material refractive index and optimizing the design of the plane-concave lens of the negative refractive grating. This study provides a reference for modulating the focal field of cylindrical vector beams and designing micro/nanostructured devices in related fields.