This study aims to determine the validity of the Problem Based Learning with Argumentation– Flipped Learning (PBLA-FL) model to improve junior high school students' critical thinking skills during the Covid-19 pandemic season. The validity reviewed here is content validity and construct validityoas well as the validity of PBLA-FL learning tools. The validity of the PBLA-FL learning tools consists of syllabus, lesson plans, teaching materials, student worksheets, and critical thinking skills test sheets. Data collectionowas carriedoout through a Forum Group Discussion (FGD) by presenting science education experts, science assessment experts, and science experts to test the validity of the model and the validity of the PBLA-FL learning tools. In conclusion, the PBLA-FL model was declared valid for improving junior high school students' critical thinking skills during the Covid-19 pandemic season, with the results of the content validity test and construct validity test in very valid and very reliable. criteria with reliability calculation results above 75%, and device validity. PBLA-FL learning criteria are valid and very reliable with reliability calculation results above 75%.