Police said the check dam was being constructed by the state government across the Adappar river at Kallimedu village near Vedaranyam.
Police identified the deceased as Shankar Rao (28), a worker from Andhra Pradesh.
Police said work was going on when the upper sheave of the crane attached to the hook suddenly snapped. The hook was carrying load and the broken portion fell down on the workers standing in the vicinity.
They have been admitted to the Nagapattinam government hospital.