A tunable linear cavity Er/Yb co-doped double-clad fiber laser operating in L-band, which utilizes amplified spontaneous emission (ASE) as a secondary pump source, is presented. The output wavelength can be tuned over 34 nm with power excursion of 0.4 dB by using a high birefringence fiber loop mirror as a wavelength filter. With 5 LDs side-pumping Er/Yb co-doped fiber simultaneously, an output power of 200 mW is achieved and the stability of output laser is very good.