Passive decoy state quantum key distribution (QKD) has enormous potential in high-speed applications. In this Letter, an intrinsic-stable non-Poissonian light source was implemented with Faraday mirrors and could be a crucial element in realizing passive decoy state QKD. The stable g((2))(0) was obtained through a Hanbury Brown-Twiss experiment, and the results fit well with the theoretical value according to Curty et al.'s theory [Opt. Lett.34, 3238 (2009)].