The invention discloses an intelligent automatic variable speed control system of a bicycle. The intelligent automatic variable speed control system of a bicycle includes a speed changer, a detection module, a neural network module, and a variable speed control module, wherein the detection module is used for detecting the physical condition of a rider and the bicycle condition, and generating a physical condition signal and a bicycle condition signal; the neural network module is provided with a calculating model which is formed through sample data training; the calculating model is used for acquiring the physical condition signal and the bicycle condition signal and then obtaining a speed changing signal of the current bicycle through calculation, and at the same time, the calculating model is updated by means of the physical condition signal and the bicycle condition signal; and the variable speed control module is used for controlling speed changing of the speed changer according to the speed changing signal. The intelligent automatic variable speed control system of a bicycle integrates the data of bicycle with the data of human body to realize automatic intelligent accurate speed changing through calculation and analysis, and has the advantages of improving riding balance, improving riding safety, and greatly improving the riding experience; and the intelligent automatic variable speed control system of a bicycle provides an automatic gear shifting strategy of a BP neural network, and can preferably solve the optimum shift identification problem, and can timely and accurately satisfy the requirement for automatic speed changing of the bicycle.