This　paper　focuses　on　the　online　energy-saving　operation　control　problem　for　passenger　and　freight　trains　running　in　a　single-track　railway　line.　Firstly,　we　design　a　centralised　optimisation　method　to　generate　energy-saving　reference　profiles　for　both　passenger　and　freight　trains,　in　order　to　improve　the　punctuality　of　passenger　trains　and　to　reduce　the　total　running　time　of　freight　trains　in　a　central　way.　Secondly,　we　propose　the　distributed　model　predictive　control　(DMPC)　based　online　trajectory　optimisation　problems　for　both　types　of　trains,　subject　to　their　respective　operational　constraints　including　safety,　punctuality,　static　speed　limits　and　temporary　speed　restrictions.　Then　we　formulate　an　online　train　operation　control　algorithm　based　on　the　centralised　optimisation　method　for　the　initialisation　of　train　trajectories　and　the　DMPC　method　for　the　online　trajectory　planning.　Finally,　the　proposed　algorithm　is　applied　to　case　studies　of　passenger　and　freight　trains　in　a　single　track　railway,　and　the　numerical　simulation　results　show　that　the　proposed　algorithm　can　realise　online　control　for　energy-saving　train　operation　in　the　presence　of　input　disturbances　and　temporary　speed　restrictions.