Andre Drummond just saved his son's life ... with the Philadelphia 76ers center springing into action after the child accidentally fell into a pool -- and the footage is terrifying.

The 28-year-old NBA champ just posted surveillance video of the incident -- with family members hanging together around the pool at his home ... when his 2-year-old son, Deon, tripped into the water.

The 6'10", 280-lb. baller -- completely clothed from head to toe -- dove right into the water without hesitation and scooped Deon out of the water ... with the other family members coming to assist.