The magnetic force is one of the concepts in physics that need good mathematical modeling and representation ability to understand. This article presents new learning model to help the student understand this concept with various representation, knowing by doing, and accommodate their mathematics modeling ability. GIMuR model has five phases, namely: (1) Organization and orientation, (2) Sequence and hypothesis, (3) Investigation, (4) Representation, and (5) Evaluation and reflection. The analysis focused on the effectiveness of GIMuR model, the activities of teachers and students during learning, and how mathematical modeling of students and their representation in understanding the magnetic force. The effectiveness of the GIMuR model was tested using a t-test with one tail. Quantitative data in the form of test results and observation of learning implementation while qualitative data in the form of student interviews. The research results indicate that: 1) learning magnetic force by using GIMuR model effectively to improve students' mathematical modeling ability; 2) teacher and student activities in all step of GIMuR model were good categories in rate; 3) teacher should back to basic concept of vector rules before using various hand rules and guided student to reveal the problem in the form of field line diagram sketch and formulas as a way to train students' thinking skills. These results showed that GIMuR could be an alternative model in magnetic force learning and enhanced students' mathematical modeling ability.