This paper discribes the measurements of Rydberg energy levels of Ru in 4d7(4F) ns (n=28-45) and 4d7(4F) nd (n=26-48) series by means of laser resonance excitation-electric field ionization method. The first ionization potential of Ru has been determined by nonlinear fitting program. These energy levels and relevant quantum defects have been calculated by using relativistic self-consistent field method The theoretical results are coincident with the experiments very well. Besides, the first ionization potential drawn from this papes has been compared with the existing data.