Cancer imaging and therapy in the second near-infrared (NIR II) window have gained increasing interest owing to the high light penetration depth and minimal optical scattering in the NIR II region (1000-1350 nm). Meanwhile, integrating multiple diagnostic and therapeutic functions into one simple nanoparticle system is of vital significance for cancer theranostics. Herein, we prepare worm-like platinum (Pt) nanoparticles (Pt nanoworms) in a facile way. The Pt nanoworms with surface modification show long blood circulation, high tumor accumulation, and negligible toxicity. With high optical absorption in the NIR II region and strong X-ray attenuation abilities, the Pt nanoworms serve as a good photoacoustic agent and CT contrast agent. Meanwhile, the tumor growth is completely inhibited by using mild photothermal therapy and radiotherapy due to the photothermally improved hypoxia and Pt increased X-ray absorption. Therefore, our work presents a biocompatible platinum nanoparticle system that is promising in image-guided tumor therapy.