A sample stacking method using on-line automatic solid phase extraction coupled to nonaqueous capillary electrophoresis, and an interface structure between a solid-phase preconcentration cartridge and a capillary therefor. The sample analysis method using solid phase extraction coupled to nonaqueous capillary electrophoresis by connecting a solid-phase preconcentration cartridge with a capillary includes: extracting a sample on a solid phase; injecting an elution solvent at an outlet terminal of the capillary, the elution solution desorbing analytes adsorbed onto a solid-phase material of a solid-phase preconcentration cartridge; and injecting a nonaqueous buffer solution from the outlet terminal of the capillary to push the elution solvent to the solid-phase material.