Let　??　be　a　Grothendieck　category,　?　an　infinite　regular　cardinal.　We　investigate　the　?-purity　of　??,　and　the　?-pure　acyclic　complexes　in　C(??).　Using　the　?-presentable　objects,　we　verify　that　the　class　of　?-pure　acyclic　complexes　is　a　thick　subcategory　of　homotopy　category.　Then　we　construct　?-pure　derived　category　naturally.　Through　some　specific　constructions,　we　get　that　bounded　above　?-pure　derived　categories　coincide　with　specific　homotopy　categories.