Based on engineering practices of unbonded prestressed concrete (UPC), some questions are discussed. Main results about experiment research by writer are introduced. 1）Model test for UPC frame ； 2)M-Φcurve of member5 ;3)Earthquake property of UPC frame; 4)Design suggest to increase stress coefficient of concrete crack. Engineering property of UPC is analyzed and induced. 1)Characteristic of UPC floor system； 2) Advantage and defect of UPC than PC; 3)Key to structure design of UPC frame.