In this paper, comprehensive experimental characterization is conducted for flexible radio frequency (RF) monocrystalline silicon nanomembrane (SiNM) diodes under various bending conditions: convex and concave bendings, paralleled and perpendicular to the diode current flow direction. The flexible diodes indicate significant/slight performance dependence with compressive/tensile bending strains paralleled to or tensile/compressive strains perpendicular to diode current flow direction. Physical and device models are employed to study the underlying mechanism, and demonstrate the dominant changing factor of flexible SiNM diodes under bending conditions. The study provides guidelines for designing and using monocrystalline SiNM diodes for bendable monolithic microwave integrated circuits.