The invention discloses a fatigue strength testing machine of bicycle brake steel cable joints and is applied to perform brake motion on bicycle brake steel cable joints during a bicycle brake steel cable product test. According to requirements of a standard, the structure of the testing machine is designed in such a way that an eccentric wheel (1) is circular, the eccentric wheel is connected with a crank connecting rod (2) and a guiding axle (3), and the eccentric wheel rotates to drive a brake handle (5) to perform up-and-down reciprocating motion. After a guiding wheel support (10) installed on a support (11) enables a steel cable and sleeve (8) to be connected with a counterweight (13) through a guiding wheel (9), the counterweight is arranged in a vertical direction, the brake handle (5) is driven to perform the up-and-down reciprocating motion through the rotation of the eccentric wheel (1), and thus a fatigue test is carried out on the steel cable joints of bicycle brakes. The structure of the testing machine can conveniently and flexibly carry out tests of brake steel cables with various specifications, the structure is ingenious, the test conditions are stable, the requirements of the national industrial standard are met, the testing machine is simple and reliable, the installation is simple, the adjustment time and energy are reduced, the work efficiency is improved, and the operation process is greatly simplified.