Workforce migration plays a strong role in reallocating productive resources and provides important clues for understanding socio-economic dynamics. In this paper, we demonstrate that like a natural shock, the Spring Festival in China culturally drives workforce to travel between workplaces and hometowns, and hence the resulting trajectories in online social media open an unparallelled window to explore laws in nation-wide workforce migration. To understand the dynamics behind workforce migration between Chinese cities, a prediction model is built by profiling the tradeoff between interest articulation and cost elusion in migration decision. Interesting migration patterns are further revealed and economic implications beyond these patterns, like the filter effect of labour market and the agglomeration effect of core cities, are fully explored, which is of great help to understand different roles of Chinese cities in their own and regional economic developments. To our best knowledge, our work is among the few studies that can leverage the full data in a social media platform for comprehensive investigation. •We explore workforce migration on social media during the Spring Festival.•A prediction model is built by profiling core driving forces in migration decision.•Mainstream patterns in inter-city workforce migration are revealed.•Malfunction of megacities in regional development is explored.•Agglomeration effect and filter effect are unveiled for policymaking in regional economic development.