The invention disclose an interface circuit provided with an optical fiber interface and used for detecting the velocity and position of a high-voltage synchronous motor, and belongs to technical field of motor rotating velocity detection. The interface circuit comprises a motor-side coded disc encoder electro-optic conversion unit and a control system-side photoelectric conversion and position-velocity calculation unit, wherein the motor-side coded disc encoder electro-optic conversion unit is used for converting electric signals into optical signals, an optical fiber transmits the optical signals to the control system-side photoelectric conversion and position-velocity calculation unit, and the rotating speed and direction of the motor are calculated out after photoelectric conversion; an absolute optical encoder adopts an SSI communication module; a clock signal is generated, a data signal is received, and the position of the motor is calculated out. The interface circuit has the advantages that both two types of interfaces such as an incremental photo-electricity encoder and the absolute optical encoder are adopted and can be selected according to conditions; the optical fiber is adopted for transmitting the coded disc signals, so that impact of electromagnetic interference on a coded disc transmission line under a high-voltage heavy-current condition is avoided.