用四大经典理论、莫尔强度理论和质点平衡强度理论的准则和强度条件，对单向拉压、二向拉压、纯扭转等已被认定的实验现象进行对比，对低、中碳钢重新做了纯扭转求最大屈服剪应力实验。发现质点平衡强度理论的符合率较高，13个实验中的有12个符合。尤其是拉伸—剪切使剪切破坏试验变得容易，压缩—剪切使剪切破坏试验变得困难的实验现象与质点平衡强度理论完全符合；莫尔强度理论也只有当拉伸和压缩极限强度不同时才能符合；其他强度理论都与此实验不符合。特别是当三向等应力拉伸（或压缩）时第三强度理论出现相当应力为零；三向等应力拉伸（或压

In this paper, a comprehensive analysis and comparison is fulfilled between the four classical intensity theories, Mohr´s intensity and a new balance particle intensity theories. A comparative study is developed between the test results of pulling or pressing in single direction and double directions. It is shown that the new balance particle intensity theory is more coincident with the test results than other five intensity theory. Especially, the intensity formula of pulling (bending)shear (torsion) deduced from the particle balance theory can easy explain the phenomena that pulling makes the destructions easy and suppression makes the destruction hard to achieve. This phenomenon cannot be well explained by the four classical intensity theories and Mohr’s intensity theory. The particle balance intensity theory clarifies the misunderstanding that if the equivalent stress is zero, the third and fourth intensity theory regard that the beam under three or fourdirections cannot be destroyed whatever the force is. The balance particle intensity theory figures out a contrary conclusion with the third intensity theory and fourth intensity theory.