In order to achieve high-precision interferometric measurement of physical quantities such as step height and absolute distance, etc, an optical fiber laser was constructed which includes multiple fiber laser resonators and can emit several wavelengths simultaneously. The erbium-doped fibers were used as gain material in each laser resonator, and the fiber Bragg gratings were employed as wavelength-choosing elements. By changing the Bragg wavelength of a fiber Bragg grating, the wavelength emitted from the corresponding resonator can be changed. Each of the cavities was independent and all of the cavities were overlapped each other. In the overlapped part, optical fiber couplers were used to configure sub-cavities and thus each resonator can emit single longitudinal mode laser. The experimental results show that each of the resonators can emit single longitudinal mode laser with stable power and stable wavelength. And the stability of each wavelength can be less than 0.01nm within 4h. This design is helpful to the research of tunable single longitudinal mode multi wavelength fiber laser.