A curtain reel structure for rapidly positioning and locking a reel seat within a curtain rail, comprising at least one reel device for engaging in a curtain rail, each of the at least one reel device comprising: a winding spool having a first axial part and a second axial part opposite to the first axial part for winding a string; a reel seat having a first engaging part, a second engaging part opposite to the first engaging part for respectively engagement with the first axial part and the second axial part of the winding spool, and a neck part disposed at a first side surface of the first engaging part, wherein the first engaging part is provided with two locking slots on a second side surface thereof for communicating with the neck part, and wherein the neck part is provided with a pivot member on one side thereof; a removable lock element pivotally connected to the pivot member and having two pivot ears at one end thereof for correspondingly assembling to the pivot member, wherein the two pivot ears are provided with at least one annular pushing portion and at least one recess on the at least one annular pushing portion; a flexible member engaged at the other side of the neck part and having an inner annular portion to sleeve on the neck part, two flexible sheets corresponding to the two locking slots for engaging with the two locking slots, and at least one protrusion corresponding to the at least one annular pushing portion or the at least one recess of the two pivot ears for being supported by the at least one annular pushing portion or engaging with the at least one recess of the removable lock element so as to allow the flexible member to be in the neck part or out of the neck part, respectively. a winding spool having a first axial part and a second axial part opposite to the first axial part for winding a string; a reel seat having a first engaging part, a second engaging part opposite to the first engaging part for respectively engagement with the first axial part and the second axial part of the winding spool, and a neck part disposed at a first side surface of the first engaging part, wherein the first engaging part is provided with two locking slots on a second side surface thereof for communicating with the neck part, and wherein the neck part is provided with a pivot member on one side thereof; a removable lock element pivotally connected to the pivot member and having two pivot ears at one end thereof for correspondingly assembling to the pivot member, wherein the two pivot ears are provided with at least one annular pushing portion and at least one recess on the at least one annular pushing portion; a flexible member engaged at the other side of the neck part and having an inner annular portion to sleeve on the neck part, two flexible sheets corresponding to the two locking slots for engaging with the two locking slots, and at least one protrusion corresponding to the at least one annular pushing portion or the at least one recess of the two pivot ears for being supported by the at least one annular pushing portion or engaging with the at least one recess of the removable lock element so as to allow the flexible member to be in the neck part or out of the neck part, respectively.