Abstract:An inequality constrained rank deficient adjustment model is proposed and on its basis the algorithm which is simple and easy to implement is designed. In the algorithm the reference condition is treated as a virtual observation and by using iterative Gaussian elimination to distinguish active or inactive constraints based on KuhnTucker condition, and then the inequality constrained model is transformed into equality constrained rank deficient adjustment model. In addition,an example of level network is given to prove the feasibility and correctness of this algorithm.