A tunable multiwavelength Brillouin/erbium fiber laser with double-Brillouin-shift spacing is experimentally demonstrated. The compound ring cavity configuration formed by a 3 dB coupler confines the odd-order Stokes signals to circulate in a cavity and provides the initial Brillouin pump and even-order Stokes signals to be coupled out. Then multiwavelength outputs with double-Brillouin-shift spacing are achieved. The output characteristics of the fiber laser are analyzed under different Brillouin pump powers and 980 nm pump powers. At the Brillouin pump power of 10 dBm and the 980 nm pump power of 110 mW, 6 output channels with 0.176 nm channel spacing from 1555 nm to 1565 nm are achieved.