Abstarct: Sustainability of agriculture requires proper management of water and fertilizer in agricultural fields. Nowadays fertigation system is the effect method of application of nutrients and water for plants. This research has been conducted in Bastam Agricultural Center for evaluation of fertigation elements with studying potassium movement, potassium leaching and drainage water with modeling approach. Selected crop was green peeper and selected model was Hydrus-2D. Soil texture of experimental field was sandy loam. A complete drip fertigation system with 1 centimeter diameter lateral and 4 l/h emitter discharge developed in field. Results of research showed that average crop yield in drip fertigation treatments was 47 t/h which was 51 percent more than yield of basin irrigation system. Simulation of potassium movement in soil laxyers showed that maximum amount of distributed potassium concentrated in middle soil laxyers corresponding crop root zone development in whole crop growth season. Potassium leaching estimated with two method of weekly fertigation 10 minute before and after fertigation. Results of potassium leaching study reveled that in weekly fertigation 10 minutes before irrigation method, potassium leaching was 3.5 percent less than another method. Another result showed that in fertigation system potassium leaching was 32 percent less than basin irrigation. The last result of research reveled that drainage water below crop root zone in basin irrigation was 55 percent of distributed water but in fertigation system it was only 2 percent indicating drainage water of basin irrigation was such more comparison with drip fertigation system.