We measured the time-integrated, spatially resolved spectra of soft x rays emitted from laser-induced aluminum plasma to characterize its spatial features. The plasma was excited by an intense femtosecond-laser pulse with a controlled artificial prepulse at intensities of 9.9×1015 and 6.4×1014 W/cm2, respectively. The dependence of the spectra on the time intervals between the main pulse and the prepulse was obtained for delay times of 0–3 ns. The strongest emissions in soft x-ray range occurred in a narrow region less than 50 μm from the target surface. In contrast to the continuum spectrum, the prepulse technique causes the Al3+2p6-2p53s emission to extend more than 600 μm from the target surface. We showed that the line emission can be separated spatially from the other continuum component of the emission spectra and that the extension length increased with increases in the pulse-separation time.