Duration of public attention on certain issues is an important metric to evaluate quality of public discussion. This study, employing public search records of 121 public issues on search engines from 2010 to 2016, reveals that the duration of public attention has been slowly but signifcantly shortened in the past seven years. Even after controlling variables, including event type and number of popular events, the decreasing trend of public attention is still signifcant. This study expands the conceptualization of "public attention", which further widens the research horizon of public attention on public issues. This study is of enlightening and pioneering signifcance for exploring agenda setting theory in the era of new media.