In　this　paper,　we　investigate　the　performance　of　the　M-ary　differential　chaos　shift　keying　(M-DCSK)　modulation　in　a　simultaneous　wireless　information　and　power　transfer　(SWIPT)　decode-and-forward　cooperative　system　over　multipath　Rayleigh　fading　channels,　where　decoding　cost　is　non-negligible　and　power-splitting　(PS)　mode　is　considered　at　the　relay.　Moreover,　we　derive　the　bit-error-rate　(BER)　expression　of　the　investigated　system　over　multipath　Rayleigh　fading　channels.　Furthermore,　we　analyze　the　impact　of　critical　parameters　on　the　system　performance　and　find　that　there　exists　an　optimal　value　of　the　PS　ratio　at　the　relay　to　obtain　best　BER　performance.　Theoretical　and　simulated　results　illustrate　that　the　proposed　system　is　superior　to　the　conventional　M-ary　DCSK　systems,　and　achieves　comparable　performance　as　the　counterpart　without　decoding　cost.