The invention discloses a traversing luffing method of a large-sized bridge erecting machine. The bridge erecting machine is slidably erected on a cross beam through middle supporting legs. The traversing luffing method comprises the following steps: 1, sliding the cross beam from the left side of a bridge to the right side of the bridge by using a steel rail. By the traversing luffing method, operation is convenient, the cost is low, the bridge erecting machine is not required to be hoisted, redetached and remounted, slippage of the cross beam in position in the case of no lifting equipment is achieved, and quick and convenient traversing luffing of the bridge erecting machine is achieved.