The photorefractive index change of iron-doped lithium niobate crystal induced by high power ultrashort pulse laser irradiation is calculated in semi-quantitative and verified in experiment. By theoretical calculations, the refractive index decrease of the iron-doped lithium niobate crystal which is induced by the high power ultrashort pulse laser (0.33 mJ, 10 ps at 527 nm) about 10-4. After the relaxation of a few nanoseconds, the index decrease is reduced to 10-5. In the experiment, the same ultrashort pulse laser is used, which is flattened and its intensity distribution is spatially shaped into a right triangle, to irradiate the iron-doped lithium niobate photorefractive crystal, resulting in rectangular prism, thus 1053 nm signal light pulse through the instantaneous photorefractive prism is deflected. The refractive index decrease calculated according to the angle of deflection is about 10-5 and theoretical result is almost in agreement with experiment. This study suggests that all-optical streak camera using the instantaneous photorefractive effect of iron-doped lithium niobate is expected to achieve the measurement of time characteristics of short pulse.