Porphyra　haitanensis　with　many　bioactive　components　has　great　prospects　for　application　in　the　functional　food,　pharmaceutical,　and　cosmeceutical　industries.　In　this　study,　two　sequentially　extracted　fractions　(PhE1　&　PhE2)　were　isolated　and　structurally　characterized.　The　results　showed　that　PhE1　was　mainly　composed　of　protein　(36.82%)　and　neutral　sugar　(32.43%),　while　PhE2　mainly　contained　neutral　sugar　(58.70%).　Both　had　galactose　as　main　monosaccharides,　PhE2　also　contained　a　small　amount　of　glucose.　To　widen　the　application　of　PhEs　in　starchy　foods,　they　were　added　to　corn　starch　(CS)　system　and　co-gelatinized.　Rheological　tests　indicated　that　PhEs　could　effectively　affect　gel　strength　of　CS.　The　addition　of　PhEs　effectively　inhibited　the　content　of　leached　amylose　in　CS　gelatinization　system　except　those　at　an　addition　of　5%　PhE1　and　5%　PhE2.　FT-IR　data　suggested　that　PhE1　could　improve　the　short-range　order,　but　PhE2　showed　no　significant　effects.　SEM　images　showed　that　the　pore　wall　of　the　composites　thickened,　and　the　network　structure　became　relatively　ordered.　In　vitro　tests,　PhEs　significantly　reduced　the　contents　of　rapidly　digestible　starch,　and　PhE1　presented　better　effects.　Therefore,　PhEs　may　be　used　as　potential　materials　to　delay　the　digestion　of　CS　and　related　products.