Muon Veto System and Expected Backgrounds at DayaBay

To reach the goal of the sensitivity of $\theta_{13}$ $<$0.01 in the DayaBay experiment, we need to reduce various backgrounds to a very low level. DayaBay implements two tagging systems to detect cosmic ray induced background: 2.5 meter thick two-section water shield and RPCs. They combine to contribute a overall muon efficiency exceeding 99.5\% with an uncertainty$<$0.25\%. The muon system can also provide a spatial resolution $\sim$50cm to help distinguish fast neutron background generated from muon interactions. This talk introduces the DayaBay muon system and gives an estimate of possible background rates at DayaBay.