Saline intrusion into freshwater aquifers is one of the important and challenging issues in water resources management. This process is usually the result of human activities such as excessive exploitation, groundwater depletion, as well as natural factors such as climate change and erosion. In this study, a combined numerical simulation model with Petrov-Galerkin gridless discretization method was presented based on the multi-objective optimization model of the sloped surface algorithm. Considering the high accuracy, efficiency and time saving in modeling, the MLPG-MOIPO simulator-optimizer model can be used as an optimal model for locating wells for exploiting aquifers. The results showed that the simultaneous use of the sloped surface system algorithm and the gridless numerical method can be of great help in optimal management to reduce groundwater level drop and maximize water extraction, minimizing saltwater intrusion. In this study, in order to investigate the efficiency of the numerical simulation model based on the Petrov-Galerkin gridless method in a coastal aquifer, an example was solved and evaluated with previous works, and the results of this evaluation showed the accuracy and validity of the developed model. Also, combining this model with the simulated model revealed its applicability in the optimal management of coastal aquifers. The results obtained from the quantitative examination of the performance of the MOIPO algorithm in the values ​​of the proximity and dispersion criteria show that the multi-objective algorithm for optimizing the sloped plate system has good performance. Therefore, the combined MLPG-MOIPO model can be introduced as an efficient model in the simulation and optimization of coastal aquifers.