The invention relates to a method for predicting performance indexes in a polyester fiber spinning process, in particular to a method for predicting performance indexes in a polyester fiber spinning process based on a least square support vector machine (LS-SVM) optimized by a particle swarm optimization (PSO) algorithm improved by a power law. The method comprises the following steps of selecting production parameters, including a spinning speed, a spinning temperature, an air blowing temperature and an air blowing speed, in the polyester fiber spinning process as feature information, performing linear function normalization, and establishing an input sample dataset; determining main performance indexes, including half-fold elongation rate, irregularity of the half-fold elongation rate, breaking strength and elongation capability, influencing polyester fiber quality, performing logarithmic function normalization, and establishing an output sample dataset; and building an LS-SVM model according to the input and output sample datasets, adopting a Gauss radial basis function (RBF) as a kernel function of the LS-SVM, and selecting an optimal penalty factor C and a kernel function parameter sigma by using PSO. The PSO process is improved according to the power law, so that the optimization speed can be greatly increased and accurate prediction is realized.