The French champions hammered Barca in the last-16 first leg at Parc des Princes on Tuesday, with Angel Di Maria netting a brace to go with goals from Julian Draxler and Edinson Cavani.
No side in Champions League history has ever overcome such a deficit in a knockout tie but despite his side's huge advantage heading to Camp Nou, Emery is still wary of the La Liga giants.
"It is a great motivation to play against Barcelona, and a difficulty," the Spaniard said in quotes reported by Marca. "The game leaves a good taste in the mouth, but you have to be careful because we have 90 minutes to play.
"We have overcome them and we have made a very complete game. We have to try to maintain the level of concentration because their game is very varied.
"I'm very cautious with the next game. We have to try to continue in the same way."
Di Maria put PSG ahead with a brilliant free-kick before a good finish from Draxler doubled the lead before half-time.
Another superb Di Maria effort from range and a Cavani goal sealed the rout for the hosts.
"When we win, we all win and when we lose, we all lose," he said. "It was a great game, both individually and collectively."
The return leg iat Camp Nou is on March 8.