  In the paper, we investigate correlation between broad-line and radio
variations for broad-line radio galaxy 3C 120. By the z-transformed discrete
correlation function method and the model-independent flux randomization/random
subset selection (FR/RSS) Monte Carlo method, we find that the broad Hbeta line
variations lead the 15 GHz variations. The FR/RSS method shows that the Hbeta
line variations lead the radio variations by a factor of tau_{ob}=0.34 +/- 0.01
yr. This time lag can be used to locate the position of emitting region of
radio outbursts in jet, on the order of ~ 5 light-years, from the central
engine. This distance is much larger than the size of broad-line region. The
large separation of the radio outburst emitting region from the broad-line
region will observably influence the gamma-ray emission in 3C 120.
