The invention provides a large span truss high and low area sliding, docking and constructing method, comprising the following steps: arranging a first sliding rail at the lower layer's main structure; arranging a lower layer truss on the first sliding rail in a sliding manner; sliding the lower layer truss to a docking position; arranging a second sliding rail at the top of the lower layer truss; extending the second sliding rail to the upper layer's main structure; sliding the upper layer truss from the position of the upper layer's main structure, along the second sliding rail to the docking position; docking the upper layer truss and the lower layer truss; removing the second sliding rail. According to the invention, the existing construction means with erected scaffolding for temporary use everywhere can be replaced, which greatly improves work efficiency, shortens the construction period, reduces the construction cost, and enhances the safety coefficient. This also solves the problems of complex operations and low efficiency in the docking of high and low areas of a truss.