A method for calculating the allocation of relay resources in optical transmission network planning, which relates the field of routing planning algorithms, comprising: using a source node as a starting node, finding the farthest node which may establish an effective optical channel, configuring a relay at the farthest node and allocating a wavelength for the channel, and then iterating by using the farthest node as the starting node until a target node is reached. The manner of finding the farthest node that may establish an effective optical channel is as follows: obtaining an available wavelength set of the starting node, sequentially calculating intersections of the available wavelength set that passes through a link between two adjacent nodes until the result is empty or the path optical signal noise ratio (OSNR) from the starting node to a current node is less than a preset threshold, and then backtracking to the nearest node that is used to configure a relay. The invention improves computational efficiency without generating additional relay resources.