Whether the skill level of industrial workers can match the direction of industry development, and achieve a dynamic balance between the supply and demand of skilled labor is crucial for providing human capital support to industrial transformation and upgrading, and highquality economic development. It is clear that trade union organizations play an important role in improving the skill level of industrial workers by promoting workers' quality improvement projects, organizing labor skill contests, and carrying out mass technological innovations. Based on microdata from a survey of industrial workers in Dalian, we found that joining trade unions signifi cantly improves the skills of industrial workers, especially workers of manufacturing industry. Moreover, mechanism tests reveal that trade unions improve the skills of industrial workers through conducting vocational training. Hence, it is suggested in the study that diverse forms of vocational training should be provided to industrial workers in practice by utilizing resources of the trade unions; and the methods of evaluating skills of industrial workers should be improved. In addition, the skills of industrial workers should also be developed by strengthening cooperation with vocational schools and utilizing multi-level and diversifi ed vocational educational resources.