Based on the career competency perspective, the purpose of the present study was to explore the impact mechanism of boundaryless career orientation(BCO) on the career success of Chinese young workers in the early career stage. A two-wave questionnaire survey was conducted to collect data using a sample of 385 young workers under the age of 35. The results showed that: 1) boundaryless mindset positively predicted young workers’ subjective and objective career success, and career competencies(i.e., knowing-why, knowing-how, knowing-whom) mediated the effect of boundaryless mindset on career success; 2) organizational mobility preferences negatively predicted young workers’ subjective and objective career success, and career competencies mediated the effect of organizational mobility preferences on career success. The findings in the study revealed a double-edged sword effect of boundaryless career orientation and provided some practical inspiration for career management of young workers.