The correlation between electronic properties and epitaxial strain in a cation‐deficient system has rarely been investigated. Cation‐deficient SrVO3 films are taken as a model system to investigate the strain‐dependent electrical and electronic properties. Using element‐ and charge‐sensitive soft X‐ray absorption, V L‐edge absorption measurements have been performed for Sr1–yVO3 films of different thicknesses capped with 4 u.c. (unit cell) SrTiO3 layers, showing the coexistence of V4+ and V5+ in thick films. A different correlation between V valence state and epitaxial strain is observed for Sr1–yVO3 ultrathin films, i.e. a variation in V valence state is only observed for tensile‐strained films. Sr1–yVO3 thin films are metallic and exhibit a thickness‐driven metal–insulator transition at different critical thicknesses for tensile and compressive strains. The asymmetric response of electrical conductivity to strain observed in cation‐deficient Sr1–yVO3 films will be beneficial for functional oxide electronic devices.