Abstract: When conducting downhole surface electromagnetic wave communication, an unreasonable layout of the relay will lead to the reduction of signal strength. To address this issue, a collaborative relay transmission method for surface electromagnetic wave was proposed. Firstly, the propagation characteristics of surface electromagnetic waves were analyzed by combining numerical simulations and experiments. Then, based on the electric field integral method, a mathematical model for the relay transmission system of downhole surface electromagnetic wave was established. The impact of different relay layouts and quantities on the signal strength of receivers was analyzed. The results show that surface electromagnetic wave have smaller attenuation and higher transmission rates compared to traditional wireless electromagnetic wave, which can be an efficient mode of subsurface communication. Meanwhile, the use of collaborative relay transmission technology of surface electromagnetic wave can increase signal strength by an average of 5.91 dB, providing a new approach to increase the transmission distance of downhole surface electromagnetic wave communication.