Density　wave　oscillations　(DWOs)　of　supercritical　water　in　the　parallel　water　wall　channels　of　an　ultra-supercritical　circulating　fluidized　bed　(CFB)　boiler　were　investigated　experimentally　and　numerically.　The　variation　ranges　are　presented　as　follows:　pressure　from　23　MPa　to　30　MPa,　mass　flow　rate　from　0.06　kg.s(-1)　to　0.22　kg.s(-1),　inlet　water　temperature　from　200　degrees　C　to　370　degrees　C.　Wall　temperatures　increase　rapidly　after　DWOs　occur.　As　the　period　decreases,　the　flow　departs　significantly　from　the　quasi-steady　conditions　and　the　penetration　of　the　variation　of　the　flow　toward　the　wall　is　significantly　reduced.　A　general　calculation　model　based　on　the　time-domain　method　was　established　to　analyze　DWOs　in　parallel　channels.　Four　pulsation　patterns　were　found　during　calculation,　that　is,　pulseless　oscillation,　damped　oscillation,　self-sustaining　periodic　oscillation　with　constant　amplitude,　and　divergent　oscillation.　The　mechanism　of　DWOs　was　investigated　through　experimentally　and　numerically　results.　Results　show　that　mass　flow　rate　of　each　channel　displays　a　reverse-phase　pulsation　during　the　oscillations.　DWOs　are　intertube　oscillations　with　a　short　period　and　small　amplitude.　Increases　in　inlet　pressure　drop　coefficient　or　decreases　in　outlet　pressure　drop　coefficient　are　conducive　to　system　stability.