Rocket propulsion is a complex and hard to understand content of Mechanics subject. For better understanding and learning perception, we established the problem solving activity called “Water rocket competition”. We assigned for every class, 10 classes and 240 students, in Grade 10 at Mahidol Witthayanusorn School for creating two home-made water rocket bottles for their class. The competition was held at the evening at February 18, 2016. The rule were the student have to launch rocket 2 time for aiming to target and got a score. After a competition, we assigned student for descripting their rocket by Physics perspective, the pros and cons of their rocket. The result showed that the average of the perception is 4.36 of 5 full scale. The students had fun about this completion and they can better explain the rocket propulsion.