McLaren leads the constructors' championship thanks to Button's third place in Australia, but Boullier accepted the team needs to improve its MP4-29 dramatically if it is to retain that position and take the fight to the pacesetting Mercedes team.
"They [Mercedes] are very fast, so clearly they are one big step ahead of everybody," Boullier added.
"We'll do our best. We are putting things in place and working and making sure we can recover on the development and also work on next year's car so we can keep up.
"The guys did a brilliant job, because both cars are in the points, they are big points and they finished the race.
"[But] the target is also to lead the championship after the last race."