A fast installation mechanism for a faucet includes a locking inner core, a fixing core, and a base. The locking inner core is a tubular member. An external thread is formed on an outer wall of the locking inner core. An upper end of the locking inner core is fixedly connected to a faucet body. A lower portion of the locking inner core is screwed into the fixing core. The base is sleeved on a lower portion of the fixing core. At least two elastic pieces on the fixing core extend out of at least two windows of the base, respectively. The installation is quick and easy, and the operation is convenient.