The invention discloses a solar energy sea water desalinating device which comprises a sea water heater and a condensing heat exchanger. The solar energy sea water desalinating device is characterized in that the sea water heater is composed of a sea water collection tank and a crown solar heat collector covered on the sea water collection tank, the condensing heat exchanger leads in sea water by a sea water inlet and leads the sea water into the sea water collection tank by a sea water supply pipe communicated with the sea water collection tank; the crown solar heat collector is composed of a plurality of transmitting glass; each transmitting glass is a biconvex mirror, and sunlight projecting the surface of each transmitting glass is respectively focused on sea water in the circular seawater collection tank, the top of the crown solar heat collector is connected with the condensing heat exchanger by a communicating pipe, and stream evaporated by the sea water collection tank is guided into the condensing heat exchanger to be output through a fresh water pipe after being condensed into fresh water.