This research was carried out to analyze the effect of Group Investigation (GI) model on the student problem solving ability and students academic achievement on the digestive system material for students grade 8th junior high school 2 Belimbing Hulu. In this study we used quasi experimental design according to the quantitative research methods, pretest-posttest using rubric to test the effect of Group Investigation (GI) learning model on the student problem solving ability and students academic achievement. The result of this research showed that the Group Investigation (GI) learning model improved the student problem solving ability and students academic achievement.. The increase of problem solving ability of students treated with "Group Investigation" (GI) model was 68.65% and the students' cognitive learning result was 47.73% higher than the conventional learning model of 38.37% for problem solving skills and 23.60 % for cognitive learning outcomes. Based on the research results it can be concluded that Group Investigation (GI) learning model has the potential to improve the student problem solving ability and students academic achievement. It is recommended that teachers implement Group Investigation (GI) learning model in schools consistently because it improves effectively on the student problem solving ability and students academic achievement.