Potassium tantalate niobate (KTN) electro-optic deflection devices attract much attention in recent years due to the advantages of large angle, low voltage, no inertia, and small size. The research progress of KTN crystal devices and applications at home and abroad is briefly reviewed. The basic principles of electro-optic deflection based on the space charge, composition gradient, and temperature gradient of the crystal are described. The characteristic parameters and main influencing factors of deflection properties of the devices are discussed. Several kinds of components and application examples based on KTN electro-optic deflection are introduced and the current problems and future trends are also summarized.