The present invention relates to prestressed composite truss girder and construction method of the same. The prestressed composite truss girder of the present invention comprises a concrete bottom plate having structure of composite truss; a lower-chord member being composed of prestressed concrete wherein prestress is induced to resist against the elongation strength generated when composing and not composing and to reduce the droop occurred at the state of composition and having perpendicular and horizontal cross-section of certain shape and certain length; web members wherein vertical chords and diagnal chords composed of rolled steel to upper plate of said lower-chord member; and upper-chord member combined with said web members along the longitudinal direction of said lower-chord member to resist against the compressive force generated before said concrete bottom plate being composed.