This study investigates vortex-induced vibration (VIV) characteristics of double free-hanging water transmission pipes, which are crucial for temperature difference energy harvesting platforms. Compared to single pipe, double pipes could offer higher transport efficiency and cost-effectiveness. In this paper, Model experiments were conducted to analyze VIV characteristics of the double free-hanging pipes and a method for identifying vortex-induced loads for large displacements and small deformations was proposed. A comparative analysis of the VIV characteristics of double free-hanging pipe and the single pipe was performed, leading to the following conclusions: Findings show that VIV displacement amplitudes of double free-hanging pipe are similar at low flow velocities but differ with those of single pipe at high velocities. The double free-hanging pipe is more prone to instability in VIV, including traveling waves and multi-frequency responses. And it is found that the VIV frequencies of double free-hanging pipe can be predicted by the same Strouhal number as the single pipe. Additionally, a significant difference in the added mass coefficient affects natural wet frequency adjustment for VIV resonance.