(only 4 data points for 3C390.3 shown in Figure 8 in Peterson et al. 2004). In the paper, we will carefully re-check the correlation for 3c390.3, because among the well-mapped objects, 3c390.3 is the unique double-peaked emitter.

In the paper, we check correlation between line width and line flux, rather than to check correlation between size of BLR and line width, in order to obtain abundant data points. This paper is organized as follows. Section 2 gives our data procedures and main results. Section 3 shows our discussions and conclusions. Here, cosmological parameters $H_{0}=70{\rm km\cdot s}^{-1}{\rm Mpc}^{-1}$, $\Omega_{\Lambda}=0.7$ and $\Omega_{m}=0.3$ have been adopted.

Main Results
============

All public spectra of 3C390.3 can be collected from the AGNWATCH project (http://www.astronomy.ohio-state.edu/\~agnwatch/), which is a consortium of astronomers who have studied the inner structures of AGN through continuum and emission-line variability. Detailed descriptions about observational instruments, techniques and procedures to reduce the spectra of 3C390.3 can be found in Dietrich et al. (1998), which will not be described any more. Here, we mainly show our procedures to measure line parameters (line width and line flux) of the double-peaked broad lines of 3C390.3, and show our results about correlation of the line parameters.

Line 