A figure-8 cavity laser was designed. A section of polarization maintaining erbium-doped fiber was pumped by a 980 nm pumping source,and then the double-pulse output of 10 MHz repetition frequency was obtained. To test the constitute of double-pulse,an erbium-doped fiber amplifier,a polarization controller and a the polarization splitter were placed at the laser output. At different ports of the polarization splitter,different single pulses were obtained. It is proved that the double-pulse is made up of single pulse with different polarization states.