This research aims to implement the guided inquiry learning model to improve the understanding of concepts and critical thinking skills of Vocational High School (SMK) students. The quasi-experiment method with the randomized pretest-posttest control group design was used to obtain data from students of one of the Vocational High Schools (SMK) in Bandung, West Java, Indonesia. The sample consisted of 28 experiment and control class students that carried out a guided inquiry and conventional learning, respectively. The result shows an average increase in understanding of physics concepts and critical thinking skills of the experimental class by 0.71 (high category) and the control class by 0.28 (low category). Based on the average test results using the independent sample t-test method, the understanding of physics concepts and the critical thinking skills of the experimental class was eminent to the control class. Furthermore, the research instruments were tests of understanding concepts and critical thinking skills with an average increase of 0.71 in the high category and 0.28 in the low category, respectively. The result showed that the implementation of guided inquiry learning models has the ability to significantly improve the understanding of static fluid concepts and critical thinking skills of Vocational High School students compared to conventional learning. This was because it provided the opportunity for students to independently construct a concept through problem presentation, formulation of hypotheses, data collection, analysis, and conclusions.