We propose and demonstrate a broadband tunable single-longitudinal-mode (SLM) erbium-doped fiber laser based on a microfiber knot resonator (MKR). The MKR is made from a double-ended fiber taper and employed for SLM filtering based on the Vernier effect. An unpumped erbium-doped fiber is used in the fiber laser cavity to suppress mode-hopping for a stabilized SLM laser operation. When combined with an optical fiber filter, widely tunable SLM laser generation is achieved. The proposed SLM laser can be tuned from 1545 to 1565 nm with a high side-mode suppression ratio of about 55 dB and a high stability.