For the first time, to the best of our knowledge, a high stability half-open cavity multiwavelength random erbium-doped fiber laser (MW-REDFL) using distributed Rayleigh backscattering feedback in a 2 km long single-mode fiber together with a reflecting comb-filter of six-superimposed fiber-Bragg-gratings (6SI-FBG) was demonstrated experimentally. We achieved six lasing wavelength-channels at ∼2 nm spacing, with a maximum peak power difference of ≤0.930 dB for all six channels and a peak power fluctuation of ≤1.101 dB for each lasing channel in a 80 min time span, a wavelength fluctuation of ≤0.032 nm for each lasing channel in an experimental time of >1.5 h, and an output power fluctuation of ≤0.05 dB in a 4 h time span at the pump power of either 100 mW or 200 mW. At the frequencies larger than 100 kHz, the relative intensity noises of six-wavelength lasing output are −125 dB/Hz and −120 dB/Hz for pump powers of 100 mW and 200 mW, respectively. The performances threshold as low as 23.51 mW and slope efficiency as high as 10.99% of our MW-REDFL were also achieved. Better performance could be further obtained with good temperature compensation and vibration isolation packaging for practical applications.