A　well-known　Assem-Smal　phi　theorem　on　tilting　modules　plays　an　important　role　in　tilting　theory.　In　this　paper,　we　prove　that　a　version　of　Assem-Smal　phi　theorem　still　holds　in　the　category　of　comodules.　Following　this　result,　we　characterize　the　tilting　torsion-free　classes　in　the　category　of　comodules　using　the　precover　theory.