A spacing-adjustable multiwavelength fiber laser based on self-excited stimulated Brillouin scattering without external Brillouin pump is proposed.The nonlinear gain of self-excited stimulated Brillouin scattering can suppress mode competition induced by homogeneous broadening of erbium-doped fiber.With the use of a birefringence fiber loop filter,the wavelength spacing can be adjusted by changing the length of the used birefringence fiber,which makes the laser more flexible.Multiwavelength output with adjustable spectral spacing from 0.8 nm to 0.076 nm is experimentally obtained.And the wavelength number increases as the decrease of wavelength spacing.