A flexible broadband linear polarization converter is proposed based on the metasurface operating at microwave band. To achieve bandwidth extension property, long and short metallic arc wires, as well as the metallic disks placed over a ground plane, are combined into the polarizer, which can generate three neighboring resonances. Due to the combination of the first two resonances and the optimized size and thickness of the unit cell, the polarization converter can have a weak incident angle dependence. Both simulated and measured results confirm that the average polarization conversion ratio is over 85％from 11.3 GHz to 20.2 GHz within a broad range of incident angle from 0° to 45°. Moreover, the proposed polarization converter based on flexible substrates can be applied for conformal design. The simulation and experiment results demonstrate that our designed polarizer still keeps high polarization conversion efficiency, even when it adheres to convex cylindrical surfaces. The periodic metallic structure of the designed polarizer has great potential application values in the microwave, terahertz, and optic regimes.