A new multi-wavelength solar telescope, Optical and Near-infrared Solar Eruption Tracer (ONSET), is constructed by Nanjing University, being run in cooperation with Yunnan Astronomical Observatory. ONSET is able to observe the Sun in three wavelength windows: He I 10830 Å, Hα and white-light at 3600 Å or 4250 Å. Full-disk or partial solar images with a field of 10 arcmin at three wavelengths can be obtained nearly simultaneously. It is designed to trace solar eruptions with high spatial and temporal resolutions. This telescope has been installed at a new solar observing site near the Fuxian Lake, Yunnan Province. The site is located at E102N24, with an altitude of 1722 m. The seeing is stable and very nice. We give a brief description of the scientific objectives and the basic structure of ONSET. Some preliminary results are also shown.