  We described a novel technique that can find the zero-field for unshielded
laser-pumped atomic magnetometer using atomic signal itself. By comparing light
density of pump beam after atomic vapor cell, it is decided which direction to
move the compensation magnetic field and whether to increase or decrease the
converging step length. The zero-field is found in less than 18s and the step
length after converging is smaller than 10nT, 10nT and 40nT for x, y and z
axes, respectively, limited by 50Hz noise in the lab environment.
