Prestrain affects the performance of dielectric elastomer actuators so much that rare actuators is used before pre-stretching. In this article, the author made a series of circular actuators with acrylic VHB4910 and graphite mixture electrodes, and performed contrast experiments, under non-prestrain, uniaxial prestrain and equibiaxial prestrain, respectively, to figure out the changing of area strain against prestrain. Result of experiment indicates that the film actuator obtains the highest output strain while applying equibiaxial prestrain. An optimum prestrain ratio of actuators, in this research, occurs between 150%~200% under equibiaxial prestrain condition. This result has practical value in the future design and use of dielectric elastomer actuators.