This paper is concerned with the constrained approximate null controllability of heat equation coupled by a real matrix
P, where the controls are impulsive and periodically acted into the system through a series of real matrices
. The conclusions are given in two cases. In the case that the controls act globally into the system, we prove that the system is global
... [Show full abstract] constrained approximate null controllable under a spectral condition of P together with a rank condition of P and ; While in the case that the controls act locally into the system, we prove the global constrained approximate null controllability under a stronger condition for P and the same rank condition as the above case. Moreover, we prove that the above mentioned spectral condition of P is necessary for global constrained approximate null controllability of the control problem considered in this paper.