Disclosed are a variable-diameter cannula device (15) and a puncturing device. The variable-diameter cannula device comprises a variable-diameter cannula assembly (101), a lower cover plate (104) and a lower housing (103). The variable-diameter cannula assembly (101) is clamped and fixed by the lower cover plate (104) and the lower housing (103). The variable-diameter cannula assembly (101) comprises at least one half movable cannula (111) and one half fixed cannula (112) approximately symmetrical to each other, and a film cannula (113) wrapping the movable cannula (111) and the fixed cannula (112). The movable cannula (111), the fixed cannula (112) and the thin-film cannula (113) form a hollow channel for the access of a surgical instrument. The variable-diameter cannula device further comprises a variable-diameter driving mechanism (102). Under the action of the variable-diameter driving mechanism (102), the movable cannula (111) linearly moves close to or away from a longitudinal axis (1000) along a transv
