On July 2 of a certain year in the future, monitoring stations across the United States discovered that a huge spaceship with a diameter of hundreds of miles approached the earth. The radio signals emitted by the spaceship interfered with the earth's communication satellite signals, and released several sub-spaceships with a diameter of 15 miles to fly over major cities on the earth. It was unclear whether the alien spaceship was a friend or foe, and people fell into panic and confusion. Computer engineer David (Jeff Goldblum) deciphered the radio signal sent by the aliens, which was actually a countdown signal for the attack. He managed to notify his ex-wife, Connie, the president's assistant, but it was too late. On July 3, the alien spaceship began to attack the earth, and human civilization was instantly hit and catastrophic. The president (Bill Pullman) and others evacuated to the military base and commanded the air force to fight back, but it was like hitting a rock with an egg, and it was useless. The military base was also destroyed. Only the pilot Steven (Will Smith) managed to induce an alien combat airship to crash. The survivors fled to a secret military base, where scientists have been studying an alien airship that crashed more than 50 years ago, working to find a way to deal with aliens. It is also the last hope for mankind...