propagation of a signal beam in an algaas/gaas waveguide multiple-prism light deflector is theoretically investigated by solving the scalar helmholtz equation to obtain the dependences of the temporal and spatial resolvable characteristics of the ultrafast deflector on the material dispersion of gaas including group velocity dispersion and angular dispersion, interface reflection, and interface scattering of multiple-prism deflector. furthermore, we experimentally confirm that, in this ultrafast beam deflection device, the deflecting angle of the signal light beam is linear with the pump fluence and the temporal resolution of the ultrafast deflection is 10 ps. our results show that the improvement of the temporal and spatial resolvable performances is possible by properly choosing the structural parameters and enhancing the quality of the device.