We define the projective operators for controlling unstable periodic o
rbit(UPO), and project the eigenvectors of Jacobian matrix of a system
in the direction of trajectory and in the direction perpendicular to
the trajectory. Then the two eigenvalues in the perpendicular directio
n are changed to negative ones by adjusting the controlling parameter.
So the control of UPO can be implemented. It is also down that the pr
ocedure is effective even in the presence of noise.