The invention discloses a support vector machine based automatic focusing method of ultrasonic phased arrays of ring welds. The method includes: establishing a rectangular coordinate system, taking a least squares support vector regression (LSSVR) machine as the regression model and Gaussian radial basis function as the kernel function, performing training with input and output which are subjected to standardized processing, and establishing a prediction model of LSSVR initial function; taking a generalization error calculated with a k-fold cross validation method as the target function, optimizing the LSSVR initial function by adopting an optimization method combining a coupling-simulated annealing algorithm with a grid searching method to acquire an optimal hype-parameter and an LSSVR optimization model, predicting tested data to acquire the output, performing inverse normalization processing to obtain the optimal acoustic beam path plan of a corresponding partition, performing reverse solution according to the Fermat theorem to obtain time delay, and applying ultrasonic signals to perform focusing detection on ring weld defects. By the arrangement, the method has the advantages that intelligent ring weld defect detection is realized, and detection precision and efficiency are effectively improved.