Quantitative investigations are made for the laser-duration dependence of the emission properties of high-order harmonic generation (HHG). HHG emission properties produced by few-cycle lasers show some useful characteristics. The cutoff energy is less than that by laser for infinite duration. The single energy distribution pulse decreases much faster than its duration as the laser duration grows. A two-cycle laser with carrier-envelope phase of O°can produce a single distribution pulse peaked at the laser carrier phase 1.22rad and spanned 1.18 rad with the cutoff energy 2.9Uρ + Iρ and a bandwidth 0.63Uρ, where Uρ is the ponderomotive potential of the laser field and Iρ is the atomic ionization potential.