We propose a novel tunable multiwavelength random fiber laser based on Brillouin scattering with half-open cavity, and it′s formed by total reflection of a connected 3 dB coupler and randomly distributed Rayleigh scattering in single mode fiber. When the Brillouin pump power amplified by the erbium-doped fiber amplifier is high enough, it is possible to generate cascaded high-order stimulated Brillouin scattering in the long single-mode fiber and achieve multiwavelength Brillouin random laser output. The results show that when Brillouin pump wavelength is 1530 nm, at best seven multiwavelength Stokes have been obtained from the Brillouin random fiber laser. We study the influence of the pump power on the output of multiwavelength random lasers by changing the Brillouin pump power and erbium-doped fiber pumped laser power. Additionally, by changing the wavelength of Brillouin pump, we find that the output wavelength of the Brillouin random laser can be tunable in wavelength range from 1515 nm to 1565 nm.