The invention provides an earth tunnel supporting structure passing through an existing railway and a construction method thereof. The construction method comprises the steps that guide pipe hole channels are obtained through drilling and locating guide pipes are arranged in the guide pipe hole channels; the other ends of cables of which one ends are connected with winches pass through the locating guide pipes and the cables go in from one ends of the locating guide pipes and go out from the other ends of the locating guide pipes; after the cables go out of the locating guide pipes, the cablesgo in from one ends of tool bit hole channels and go out from the other ends of the tool bit hole channels; after going out from the other ends of the tool bit hole channels, the cables are connectedwith barbs, and the winches wind up the cables to pull tool bits into a soil body; and when the barbs move to the end along slit guide pipes, the barbs are pulled out along slits, the barbs are takendown, the other ends of the cables go in from one ends of first pipe joint hole channels, go out from the other ends of the first pipe joint hole channels and then are connected with the barbs, the winches wind up the cables to pull single first pipe joints into the soil body, and the above steps are repeated until the supporting structure is completed. Through the earth tunnel supporting structure passing through the existing railway and the construction method thereof, direction deviation generated during construction of the supporting structure can be reduced, and the construction speed isincreased. The earth tunnel supporting structure passing through the existing railway and the construction method thereof have the characteristics of being simple and efficient.