A wavelength-tunable fiber laser based on a twin-core fiber (TCF) comb filter is proposed and demonstrated. The TCF comb filter is fabricated by splicing a 0.85m long TCF between two standard single mode fibers (SMFs) and with exhibits a good linear strain characteristic with a sensitivity of 1.23 pm/με. The wavelength of the laser can be linearly tuned from 1558.04nm to 1553.62nm by applying an axial strain to the TCF comb filter. The optical signal-to-noise ratio (OSNR) of the fiber laser reaches 45dB. The 3dB bandwidth is 0.02nm. The fluctuation of the laser peak in the output power and the wavelength is less than 0.5dB and within 0.05nm, respectively. The fiber laser has the advantages of having a simple structure and stable operation under room temperature.