Abstract: The identity legality of labor unions has been disputed in practice. The organizational structure and the working mechanism of three types of labor union that serve migrant workers are analyzed based on field investigation. In form，all the three types of labor union are legal-rationally legitimate in terms of identity，yet in practice，their legitimacy features can also be traditional，charismatic，or a combination of both. The practical dilemma of the three types of labor union due to their identity legality includes the insubstantiality，dependence，and lagging behind of labor union’swork and function. From Habermas’s perspective of legal legitimacy，the identity legitimacy of the three types of labor union is still in jeopardy：although empirically they are socially effective， they are faced with a legitimacy crisis in terms of specification effectiveness.

Key words: migrant labor union；identity legality；practical type