In this paper, we consider a non-overlapping domain decomposition method for solving optimal boundary control problems governed by parabolic equations. The whole domain is divided into non-overlapping subdomains, and the global optimal boundary control problem is decomposed into the local problems in these subdomains. The integral mean method is utilized to present an explicit flux calculation on the inter-domain boundary in order to communicate the local problems on the interface between subdomains. We establish the fully parallel and discrete schemes for solving these local problems. A priori error estimates in L2-norm are derived for the state, co-state and control variables. Finally, we present numerical experiments to show the validity of the schemes and verify the derived theoretical results.