In order to determine the precise effective temperature and surface gravity of warm stars, all synthetic spectral lines in the wavelength range of 4000-5700Å with T=6000-7750 K, and log g=3.5, 4.0, and 4.5 for [M/H]=0.0, Vrot=10 km s-1, and Vtubl=2 km s-1 were calculated using the SYNSPEC package(Hubeny, et al., 1995) and the Kurucz(1995) model. Then, the depth-ratios for all line pairs were investigated and we selected two and six depth-ratios appropriate for the surface gravity and temperature indicators, respectively. We plotted six grids with X- and Y-axes for the depth-ratios of surface gravity and temperature, respectively, for the simultaneous estimation of these two atmospheric parameters. This method was applied to the spectum of δ Scu for the determination of its temperature and surface gravity simultaneously.