Based on the dual transverse Pockcls effect in some crystals, a novel Electro-Optic Crystal Multiplier (EOCM) is advanced. The multiplying operation between two electric signals can be done by an electro-optic crystal in a light carrier. It is experimentally verified that EOCM is capable of being applied to make the amplitude modulated optical signal and to measure the electric power. The nonlinearity error in measuring the DC electric power by a lithium niobite crystal is less than 3.3%.