The invention belongs to the technical field of medicines and discloses a Nelarabine compound for Nelarabine composition serving as an anti-tumor drug. Nelarabine is crystalline, X-ray powder diffraction pattern obtained through measurement by Cu-K alpha rays is shown in Figure 1. The new crystal form of Nelarabine is different from the crystal form structure in the prior art, and experimental verification finds that the compound in the new crystal form is high in purity, good in fluidity and water solubility, high in stability, unlikely to absorb moisture and safe and reliable in clinical application.