Abstract: Inequality constrained adjustment model can describe the prior information in geodesy in a relatively ambiguous manner and improve the result, so it is widely used in many fields such as GPS data processing. The past methods always refer to the theory of optimization and are far away from classical adjustment. A new simple iterative algorithm that is similar to classical adjustment is proposed based on penalty functions and zero or infinite weight. Numerical simulation shows that this algorithm is simple and feasible and has good convergence. Then it is applied to a dam deformation monitoring control net, the inequality constraints of control points are established according to the terrain and we can detect the real displacement of the control points and it is more reasonable and reliable than that of unconstrained adjustment.