In　order　to　overcome　the　shortcoming　that　the　dual　distributed　sub-gradient　optimization　methods　need　to　construct　a　feasible　solution,　a　novel　distributed　sub-gradient　optimization　method　based　on　primal　decomposition　is　proposed　in　this　paper　and　used　to　solve　the　joint　dynamic　economic　dispatch　(JDED)　problem　of　multi-area　interconnected　power　systems　(MAIPSs).　Firstly,　the　centralized　optimization　model　is　established　and　decomposed　into　multiple　independent　local　areas＇　optimization　and　a　global　coordinator＇s　optimization　by　splitting　area　power　grids　and　cross-area　tie-lines.　Moreover,　the　slack　variables　and　corresponding　penalties　are　introduced　into　the　local　optimization　to　ensure　feasibility　and　optimality.　Secondly,　a　distributed　sub-gradient　optimization　method　is　proposed　to　solve　the　decomposed　model,　in　which　the　sub-gradient　is　calculated　by　using　the　dual　multipliers　from　local　optimization.　Furthermore,　in　order　to　get　better　convergence,　the　heuristic　updating　rules　for　step　size　and　penalty　factor　are　designed.　Finally,　the　numerical　tests　are　carried　out　on　two　interconnected　systems　of　different　scales,　and　results　show　that　the　proposed　method　can　obtain　a　good　feasible　solution　directly　and　has　high　computational　efficiency.　©　2021　IEEE.