A technique for controlling and mapping the optical bistability of an L-band dual-wavelength erbium-doped fiber laser (EDFL) with cascaded linearly coupled cavities was presented and demonstrated in this paper. By using a fiber loop mirror (FLM) with a polarization controller (PC) in the loop as the common mirror of the laser, we found that the bistability of the laser may be efficiently controlled by adjusting the reflectivity of the FLM which is determined by the PC state. Moreover, the bistability varies monotonically with the reflectivity of the FLM. By making use of this property, the two stable states and the two potential lasing wavelengths of the laser may be respectively mapped and switched with respect to each other by adjusting the PC for any fixed pump powers, as long as the pump power lies between the first turning point of the bistability for the maximum reflectivity of the FLM and the second turning point of the bistability for the minimum reflectivity of it.