The quality of the molten steel is usually judged by the hit rate of the endpoint. However, there are many influencing factors in the steelmaking process, and it is difficult to accurately predict the endpoint temperature and carbon content. In view of this, a data-driven Multi-Task Learning (MTL) steelmaking endpoint prediction method was proposed. Firstly, the input and output factors of steelmaking process were analyzed and extracted, and a number of sub-learning tasks were selected to combine the two-stage blowing characteristics of steelmaking. Secondly, according to the relativity between the sub-tasks and the endpoint parameters, the appropriate subtasks were selected to improve the accuracy of the endpoint prediction, and the multi-task learning model was constructed, and the model output was optimized twice. Finally, the process parameters of the multitask learning model were obtained by model training of the processed production data through the proximal gradient algorithm. In the case of a steel plant, compared with neural network, the prediction accuracy of the method proposed increased 10% when endpoint temperature error was less than 12% and carbon content error was less than 0.01%. The prediction accuracy increased by 11% and 7% respectively with the error range less than 6% and 0.005%. The experimental results show that multi-task learning can improve the accuracy of endpoint prediction in practice.