Two kinds of fiber loops are employed as cavity mirrors to setup a linear cavity tunable multi-wavelength Er-doped fiber laser. By cooling Er-doped fiber in liquid nitrogen to 77 K, employing the tunable fiber loop mirror as a output mirror,and utilizing the filter characteristic of Mach-Zehnder interferometer and the wide-band tunable reflectance feature of the tunable fiber loop mirror together, a multi-wavelength fiber laser with channel spacing of ~0.4 nm are got. A maximum number 48 of output lasing wavelengths is achieved, and the lasing multi-wavelength region can be conveniently tuned from 1525nm to 1555nm.