In Elastic Optical Networks (EONs), elastic operations have been constrained by the assumption that an optical signal has to occupy a dedicated frequency range, with no sharing of spectrum resources with other independent optical signals. Recently, the emergence of signal overlap techniques can break this traditional constraint in theory. In this study, we fully combine the characteristics of the application signal overlap technology, summarize two factors that affect the ultimate transmission distance of an optical signal as the modulation format of the optical signal and the interval between the center frequencies of the two optical signals, and make a reasonable assumption about their correspondence. On this basis, we propose a Routing, Modulation level and Spectrum Assignment (RMSA) algorithm based on Signal overlap for EONs. The paper simulates the two strategies of the algorithm and compares them with the basic algorithm without signal overlap. The results show that it can significantly reduce the bandwidth blocking probability, especially under heavy traffic load scenario.