In　order　to　coordinate　with　Soft　PLC　developing　system　running　on　PC　to　accomplish　corresponding　control　function,　compiling　system　of　Soft　PLC　was　developed.　Firstly,　the　paper　briefly　described　the　constitution　of　soft　PLC　compiling　system　as　well　as　ergodic　algorithm　of　soft　PLC　ladder　diagram　and　instruction　list.　Secondly,　it　introduced　interconversion　implementation　process　of　soft　PLC　ladder　diagram　and　instruction　list.　Via　examples,　it　expounded　design　process　of　instruction　list　grammar　of　soft　PLC,　PLC　grammar　predictive　analysis　sheet,　predictive　resolver　model　as　well　as　its　control　program　algorithm.　In　addition,　the　process　of　soft　PLC　program　syntax　analysis　was　elaborated　and　interpretation　process　of　several　common　instructions　was　illustrated.　The　emulation　results　show　that　the　compiling　system　developed　can　fulfill　interconversion　between　ladder　diagram　and　instruction　list,　and　complete　grammar　design　as　well　as　syntax　analysis　of　soft　PLC　program　and　give　correct　interpretation　of　program　instructions,　which　can　make　PC　carry　out　corresponding　control.