A tunable erbium-doped fiber laser based on cascaded filtering of Sagna c loop and Mach-ZEHNDER (M-Z) filter is proposed in this paper.In the experiment,the measured period of comb spectr a of M-Z filter is 2.2nm.A segment of 10m long polarization-maintaining fiber (PMF) is used as t he high birefringence fiber in Sagnan loop,and the measured period of comb spectra is 0.42nm.A segment of 15km long single-mode fiber (SMF) is added to the resonator to gene rate nonlinear effect and stabilize laser output.The experimental results suggest that not only the linewidth of single wavelength laser is less than 0.07nm,but also the linewidth of double-w avelength laser is less than 0.07nm.The peak powers of both the single wavelength laser and the do uble- wavelength laser are more than －17dBm,and the side-mode suppression ratios (SMSRs) of both are more than 32dB.The maximum output power fluctuations of the single wavelength laser and the double- wavelength laser are both less than 1.2dBm.By adjusting the driving voltage of M-Z filter and changing the polarization state of polarization controller (PC) in Sagnac loop a t the same time, the wavelengths of single wavelength laser and double-wavelength laser can be c ontinuously tuned within the range of 2.2nm.