The invention provides a method for preparing a titanium-magnesium composite plate by electromagnetic induction heating and different-temperature straight rolling. The method comprises the following steps: S1, plate blank pretreatment; S2, symmetric assembling and plate blank fixing; S3, gas protection: feeding inert gas into an induction heating furnace; S4, composite plate blank induction heating: using a ferromagnetic material, rapidly increasing the temperature of an iron plate by thermal effect generated by eddy-current heating, and transferring heat to a titanium plate and a magnesium plate successively from the iron plate to generate temperature difference rapidly, wherein selection of the temperature difference is determined by a used plate blank material; and S5, different-temperature symmetric rolling. By difference between thermophysical properties of materials, on the premise of low energy consumption, the purpose of rapidly forming temperature difference between the titanium plate and the magnesium plate is achieved by electromagnetic induction heating, thus, deformation resistance difference between the plates is reduced to realize coordination deformation, symmetricrolling is realized under the condition of different temperatures, the titanium-magnesium composite plate with good straightness is obtained, and the problem of severe warping and breakage of the titanium plate in the prior art is avoided.