The invention provides a wide-range composite viscosity measuring instrument for a melt. The instrument includes a cover body, a motor mounting platform, a servo motor, a hanging spring, an encoder, an encoder mounting platform, a measuring connection rod and a rotor. The motor mounting platform and the encoder mounting platform are fixedly arranged in the cover body respectively, and the motor mounting platform is located above the encoder mounting platform; the servo motor is installed on the lower surface of the motor mounting platform, and the encoder is installed on the upper surface of the encoder mounting platform; the top of the hanging spring is fixedly connected with a power output shaft of the servo motor, and the bottom of the hanging spring is fixedly connected with an encoder rotating disk; an output shaft of the servo motor is connected with the top of an encoder shell in a clamping mode, the measuring connecting rod is located on the outer side of the cover body, the top of the measuring connection rod is fixedly connected with the center of the encoder rotating disk, and the bottom of the measuring connecting rod is connected with the rotor. The viscosity measuring instrument is simple in measurement structure and high in measuring accuracy, can be applied to high-viscosity liquid, low-viscosity liquid, high-viscosity melts and low-viscosity melts at the same time, and is strong in applicability.