Understanding the characteristics of swell propagation is practical for swell monitoring, early warning and wave power generation. In this study, the attenuation rate of swell energy during the propagation process is defined. Then, the propagation, attenuation and intraseasonal oscillation characteristics of swell energy in the Pacific Ocean are analyzed based on the 40-year European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis (ERA-40). Results show that (1) The swells generated from the North Pacific Ocean westerlies (NPOW) and the South Pacific Ocean westerlies (SPOW) usually propagate to the low latitude waters of the Pacific Ocean. (2) Swells in Hawaiian waters, Cologne Islands waters and Iquique waters mainly originate from the winter hemisphere. (3) It takes approximately 8 days for the swell to propagate from the SPOW to Cologne Islands waters. It takes approximately 7.5 days for the swell to travel from the NPOW to Cologne Islands waters. (4) An obvious attenuation of swell energy of 60%-90% occurs during the propagation process. (5) Swell energies in the SPOW, NPOW, Hawaiian waters, Cologne Islands waters and Iquique waters share a common quasi-biweekly oscillation. The attenuation rate of the swell energy has a significant quasi-weekly or quasi-biweekly oscillation.(c) 2022 Elsevier Ltd. All rights reserved.