Abstract: By the popularization of structure calculating software, designers of nowadays only need to input necessary data to the computer and then get the final result of calculation and analysis. But calculating software itself is a `camera obscure' to most of the designers due to the fact that the total process of calculating and processing might be beyond monitoring and control. Structure designers must possess of realizing structure concept so as to comprehend the elementary hypothesis, calculating model and extent of application of the calculating software, therefore to make better control of strucure performance to ensure its safety, economical cost and rational quality.