In some cases 'defeat' and 'beat' mean basically the same thing - to be victorious over somebody or something. 'Defeat' is more formal, however. Also, if we are talking about a battle or warfare, you would only use defeat. "The Norman forces defeated those of Harald at Hastings." Sports: "Detroit beat Houston yesterday, 4 to 1" = "Detroit defeated Houston..." In the case where there is some race to a goal, you would only use beat. "Thomas beat John to the finish line."

defeat,一般指在战场上打败敌人。 beat后面跟人，表示在游戏或比赛中打败对方。也可以表示"连续性地击打”，如殴打，体罚等。