  Decoy state method could effectively enhance the performance of quantum key
distribution (QKD) with practical phase randomized weak coherent source.
Although active modulation of the source intensity is effective and has been
implemented in many experiments, passive preparation of decoy states is also an
important addition to the family of decoy state QKD protocols. In this paper,
following the theory of Curty \emph{et al.} [PRA, 81, 022310 (2010)], we
experimentally demonstrate the phase-encoding passive-decoy-state QKD with only
linear optical setups and threshold single photon detectors. In our experiment,
two homemade independent pulsed lasers, with visibility of Hong-Ou-Mandel
interference $0.53(\pm 0.003)$, have been implemented and used to passively
generate the different decoy states. Finally, secret key rate $1.5\times
10^{-5}$/pulse is obtained with 10km commercial fiber between Alice and Bob.
