  We use single homodyne detector to accomplish Continuous-Variable quantum key
distribution(CV QKD) in a laboratory and urban environment free-space channel.
This is based on Gaussian modulation with coherent-states in the polarization
degree of freedom. We achieved a QKD distance at 460m, at the repetition rate
of 10 kHz. We give the security of this protocol against collective attack in
the asymptotic regime. The secure key rate is 0.152 kbps at the typical
reconciliation efficiency of 0.95. The experiment setup of this scheme is
simplified and the difficulty to realize has been remarkably reduced compared
to traditional symmetric modulation ones, for example, GG02 protocol. The
influence of security key rate brought by asymmetric modulation is small in a
relative low channel loss condition in the free-space environment. This scheme
is expected to be significance meaning to the future practically utilize.
