A novel configuration of tunable single-longitudinal and single-polarization erbium-doped fiber laser is presented, while two stages of quasi-collinear acoustooptical tunable filters(AOTFs) are used as the tuning elements. An unpumped Er3+-doped fiber(low dopant) is used to narrow the linewidth and eliminate mode hopping. The theoretical calculation shows the output power is 5.5 mW and the linewidth can reach 10-4 nm level when the pump power is at 100 mW. All these data are significant for the oncoming experimental study.