Aiming at the problem that parallel flexible mechanisms applied in micro/nano-positioning fields struggle to decouple rotational motion from other degrees of freedom to form independent actuation units, the rotational motion decoupling mechanism based on orthogonal arrangements of reed-beam parallelogram mechanisms is extended. By replacing reed beams with arc beams, a series of flexible rotational nano-motion decoupling mechanisms based on arc beams are designed, and their compliance modeling and performance testing are conducted. Firstly, the configurations of flexible decoupling mechanisms with different arc beam heights were introduced. Each mechanism was composed of two identical orthogonal upper and lower parts, which fully utilized the compliance characteristics of arc beams in various degrees of freedom, enabling decoupling among multiple coupled degrees of freedom, including translational motions. Then, theoretical modeling of the flexible decoupling mechanisms was performed based on the compliance matrix method to determine their dimensional parameters and derive their output compliance. Finally, the accuracy of the theoretical compliance models was validated by combining finite element analysis with experiments, and the decoupling capabilities of different mechanisms were compared. The results showed that the relative errors between the finite element analysis and experimental results and the theoretical calculation results of each flexible decoupling mechanism's compliance were within 10%, and its decoupling performance was positively correlated with the height of arc beams on both sides. This type of flexible decoupling mechanism can be applied to the flexible mechanism design for multi-degree-of-freedom parallel micro/nano-positioning platforms, which has certain practical value.