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Free proline has multiple functions in plant cells, such as regulating osmotic potential and protecting both proteins and cell membranes. The expression of Δ1-Pyrroline-5-carboxylate synthase (P5CS), a key enzyme in the proline biosynthetic pathway, increases under drought, salt and cold stress conditions, causing plant cells to accumulate large amounts of proline. In this study, we cloned and identified the <i>P5CS</i> gene from <i>Stipa purpurea</i>, which has a full-length of 2196 bp and encodes 731 amino acids. A subcellular localization analysis indicated that SpP5CS localized to the cytoplasm. The ectopic overexpression of <i>SpP5CS</i> in <i>Arabidopsis thaliana</i> resulted in higher proline contents, longer roots, higher survival rates and less membrane damage under drought stress conditions compared with wild-type controls. <i>SpP5CS</i>-overexpressing <i>A. thaliana</i> was more resistant to drought stress than the wild type, whereas the deletion mutant <i>sp5cs</i> was less resistant to drought stress. Thus, <i>SpP5CS</i> may be a potential candidate target gene for increasing plant resistance to drought stress.