Synthetic aperture ladar(SAL) is a coherent imaging ladar which uses the the relative motion of aperture to the target and simulates apertures array with signal processing to obtain high transverse resolution. In this study， single frequency fiber laser source with narrow line width and coherent detection were employed. Transmitted optical wave was modulated with chirped signal on amplitude， and the received signal was compressed on length. The relative motion between ladar and target changes the phase of echo. Phase compensation and integration were realized by correlation operation to increase azimuth resolution. A new work style was put forward. It is convenient for solving coupling hazy problem between the range and azimuth dimension. The experiment results show that the laser intensity is modulated by chirp RF， and the range dimension compress of synthetic aperture ladar is realized.