A model tester for a low-pressure rotor system of a gear transmission fan engine belongs to the field of machinery and comprises a power part, a low-pressure turbine rotor, a support, a fan rotor anda connecting part. The power part provides power for the low-pressure turbine rotor part; the low-pressure turbine rotor part comprises two fulcrums A and B, A is located on a boss at the front end ofthe low-pressure rotor shaft, and B is located on a boss at the rear end of the low-pressure rotor shaft; the fan rotor part comprises a fulcrum C; the fulcrum C is positioned on a boss at the rear end of the fan rotor shaft; and the supporting part comprises three sets of bearing components which are respectively positioned at the positions of the three fulcrums A, B and C. All the parts are connected through connecting parts. Axes of all rotary parts in the device are collinear, and torque is input by a motor, passes through a low-pressure rotor shaft, a low-pressure turbine balance weightdisc, a low-pressure compressor balance weight disc and a gear case and finally flows to a fan rotor part. The device is simple in structure, convenient to install and capable of meeting engineering requirements, and inherent characteristics and unbalanced response of the star gear flexible rotor coupling system can be studied in a test mode.