The invention aims to provide a silicon single crystal diameter control method based on a constant-pull-speed control structure. The method comprises steps as follows: firstly, a non-linear large lagprediction model of the thermal field temperature-crystal diameter process is recognized according to thermal field temperature and crystal diameter data in a conventional silicon single crystal control structure, wherein delay parameters, input-output orders and model parameters in the prediction model are acquired through an output correlation delay determination algorithm, a Lipschitz factor and training of a stack sparsity automatic encoder, the stack sparsity automatic encoder is taken as the prediction model to be introduced into a non-linear general predictive control algorithm, and crystal diameter control is realized through the prediction model in a prediction control algorithm, feedback correction, rolling optimization and other strategies. The problems that the control effect becomes poor and control fails due to drastic fluctuation of the crystal pulling speed in the existing silicon single crystal diameter control process are solved.