The invention discloses a cast-in-situ formwork for bridge construction, and the cast-in-situ formwork comprises a bottom die and two side dies which are arranged at the left side and right side of the bottom die in an opposite way, wherein each side die comprises a side die panel, and a top flange plate and a bottom flange plate which are respectively welded on the upper end surface and lower end surface of the side die panel; the left end and right end of the bottom die are respectively fixedly provided with a plurality of bottom die ear plates which are vertically arranged upward; the outer end parts of the bottom flange plates are respectively welded with a plurality of side die ear plates which are vertically arranged upward; the bottom flange plates are arranged on the bottom die and are fixed together with the bottom die by virtue f multiple horizontal shearing bolts; each bottom die ear plate is respectively fixed together with the corresponding side die ear plate by a vertical shearing bolt; and the top flange plates which are arranged at the left and the right in an opposite way on the side die are respectively connected with each other by virtue of formwork ties. In the cast-in-situ formwork for bridge construction, the side dies not only can be used for bearing the horizontal loads such as the lateral pressure of concrete and the like, but also can be used for bearing the vertical loads such as the self weight of the concrete and the like together with the bottom die, so that a support bracket is not needed to be additionally arranged below the bottom die, and the aim of saving the space below the bottom die can be achieved.