We consider a linear-quadratical optimal control problem of a system governed by parabolic equation with distributed in right-hand side control and control and state constraints. We construct a mesh approximation of this problem using different two-level approximations of the state equation, ADI and fractional steps approximations in time among others. Iterative solution methods are investigated for all constructed approximations of the optimal control problem. Their implementation can be carried out in parallel manner.There are few results in the area of numerical solution methods for the constrained parabolic optimal control problems. One of the approaches to overcome the difficulty connected with low regularity of the solutions is using Lavrentiev regularization. This approach has been used in [6] [7]. In [8] [9] [10] [11] a priori error estimates for space-time discretizations of linear-quadratic parabolic optimal control problems have been obtained for problems.