Abstract: In order to meet the needs of users and to improve the data processing function in control surveying,we have proposed two algorithms in this paper based on graph theory.According to the observation file of control network,one is the step-by-step back-substitution algorithm,with which a set of least independent close loops in control network can be produced automatically.And the other in called combination algorithm,which is used to produce the connecting traverses.The corresponding program is developed.Finally,illustrations are given to show that the proposed algorithms are valid and effective.