Jesus refers to himself as ‘Son of Man’ 88 times in the New Testament.
1. ‘Son of Man’ was a prophetic title for the Messiah in the prophecy of Daniel: ‘there before me was one like a son of man, coming with the clouds of heaven’ (Dan 7:13-14). Jesus identifies himself with that prophecy. Likewise he called himself the ‘cornerstone’, identifying himself with Isaiah 28:16 and Zechariah 10:4, and on the Cross he identified himself as the eternal heir to King David by quoting Psalm 22: ‘My God, my God, why have you forsaken me?’
2. By calling himself ‘Son of Man’ Jesus states clearly that he is truly a human being as well as truly God. God calls the prophet Ezekiel ‘Son of Man’ 93 times, and elsewhere it is used poetically to mean simply ‘man’ (Numbers 23:19, Isaiah 56:2, Psalm 79:18). So when Caiaphas asks Jesus if he is Son of God, Jesus replies that he is the Son of Man who will be seen sitting at the right hand of God (Matthew 26:63-64). He is God and man.
Read more: Catechism 456-470.