Structural mechanics is the studies in which students must grasp physical phenomena substantially，especially students in civil and architectural engineering. In the past three years，we have given the same test of structural mechanics to the third grade students，before an experiment of construction engineering is carried out. There are serious mistakes in the test solutions，although the students could solve the problems correctly in the first grade. We fear that they might learn the solutions for several types of problems in mechanics by heart. This paper presents typical mistakes in deformed shape，bending moment diagram and maximum stress location of statically determinate beams or statically indeterminate beams. The visualized teaching system，such as a failure test system of a cantilever beam，is useful to lead to a correct understanding of structural mechanics