During the interaction of laser with solid targets, the counteracting force is generated by the plasma, which can be used as a new type source of propulsion. Compared with the chemical propulsion, laser plasma has unique advantages such as high specific impulse and large load ratio. In this paper, the momentum generated by the laser plasma is measured during the interaction of nanosecond laser pulses with aluminum, graphite, lead and CH targets. The relation of target momentum with laser focal area in atmosphere and vacuum ambient pressure is obtained,and the comparison is performed between the experimental and analytical results. It is shown that the target momentum in vacuum is different from that in atmosphere. In vacuum, the target momentum shows a dependence on the target property. These results are different from those generated by long width pulses.