A stable multiwavelength erbium-doped fiber laser has been proposed and experimentally demonstrated based on black phosphorus quantum dots (BPQDs) packaged by polytetrafluoroethylene. The laser mainly consists of a polytetrafluoroethylene packaging device of black phosphorus quantum dots (PTFEPD-BPQDs) and a Lyot filter. PTFEPD-BPQDs have the function of suppressing the mode competition and stabilizing the multiwavelength output. In the experiments, for the unpackaged BPQDs device, BPQDs will degrade and lose its function within 48 h, whereas for the PTFEPD-BPQDs, BPQDs can keep their function for more than 3 weeks. Fifteen stable multiwavelength lasing signals (MWLSs) with the wavelength space of 0.35 nm are achieved. A 10-min optically driven deposition is more conducive to the stable output of MWLSs. The wavelength offset and peak power fluctuation of the output spectrum at central wavelength are 0.1 nm and 0.9 dB, respectively.