Abstract: We have built a high-resolution system for observation of the full solar disk in the Yunnan Observatories using a 5inch solar telescope. We modified the optical system of the telescope and designed a new eyepiece system, which together with the objective lens of the telescope forms a complex imaging system. Our new system can obtain a solar image of size up to 21.4mm on the focal plane. We choose a Canon EOS 5D Mark II digital camera with 21 000 000 pixels and a maximum frame of 36×24mm² on the focal plane. The camera is suitable for exposures of 1/2000 second or 1/4000 second. We present two images obtained by the new system to demonstrate its effectiveness. The images are those of the full solar disk with sunspots present and have a resolution of about one arcsecond. In the images all sunspots existing at the observation moments are distinctly visible. The identifiable features include small sunspots and the umbra/penumbra of a large sunspot. In view of the results our system may replace a traditional sunspot observation system which requires an observer to manually trace sunspots and manually reduce recorded data. Digital data obtained by the new system can be processed by computers to find parameters about sunspots, e.g., their daily numbers, total spherical areas, and surface areas. The processing can take advantage of the sunspot model and data processor that have been used for several decades in the Yunnan Observatories. We will describe related data processing and software in another paper.