The disclosure provides an automatic and fast measuring device and method for frequency response of an electro-optic modulator. The automatic and fast measuring device for frequency response of the electro-optic modulator comprises an optical wave element analyzer and a polarization-maintaining DC optical signal source, wherein the optical wave element analyzer is used for outputting radio frequency modulation signals from a radio frequency port and transmitting the radio frequency modulation signals to each electro-optic modulator to be measured successively through 1*n radio frequency switches; the polarization-maintaining DC optical signal source is used for outputting polarization-maintaining DC optical signals, and modulating the polarization-maintaining DC optical signals into corresponding modulated optical signals through the radio frequency modulation signals in the electro-optic modulators; the modulated optical signals are output to the optical port of the optical wave element analyzer through corresponding channels of n*1 coupler respectively; the optical wave element analyzer is also used for measuring the frequency response parameter of a link to be measured, and thendividing the frequency response parameter of the link to be measured by the product of the known frequency response parameters of the 1*n radio frequency switches and the n*1 couplers to obtain the frequency response of the electro-optic modulator; and n is a positive integer greater than or equal to 2.