Abstract: Based on the synergic relationship assumption of structure among main bodies of the critical project, by taking into consideration root causing the infectious risk of the critical project and the infectious characteristics of the critical project, a structural synergistic gain model is constructed which synergizes the infectious risk of the critical project at the high limit and ensures normal and ordered construction. Through utilizing a mathematical analysis method and taking the subject behavior of the core leading factor "person" formed by the infectious risk of the critical project as the point cut, a mathematical comparative analysis is carried out based on the structural synergistic gain model of the infectious risk. The research result shows:(1) when the ratio of infectors capable of being synergized is less than the critical value, it shall hold back the infectious risk strategy by a large-scale constant-rate so as to prevent from damaging the structural balance between the infector and the other person and thus cause serious impact on the synergizer and other person unrelated or even cause local or large-area shut-down of the critical project. (2) When the oscillation period of the synergism infector is more than the critical value, it shall be not too frequent for implementing the oscillation synergism infectors so as to prevent a structural disequilibrium. At that time, the moderate oscillation synergism management can not only make the personnel structure free from collapse caused by the infectious risk but also digest and reduce the infector density in pro rata by synergism. (3) Through a comparative analysis, it is found that when the oscillation period is more than the shortest one, the oscillation synergism is better than the constant-rate hold-back; otherwise, the constant-rate hold-back is better than the oscillation synergism. Moreover, it is found that under two synergism means of constant-rate hold-back and the oscillation synergism, the critical value of the structural proportion unbalancing can be avoided between the infector and the synergizer so as to promote structural synergistic gain of the critical project. Therefore, the research not only discloses relevant mechanism of infectious risk synergism of the critical project but also en riches the coordinative management research theory. The structural synergistic gain model and its index provides references for selecting the coordinative management of the infectious risk of the critical project. It specifically inhibits and prevents the occurrence of large-scale infectious risk, protects personnel structure proportion of the critical project, reaches the effect of structural synergistic gain, protects national economic "stabilizer" and effectively promotes sound and stable development of the critical project.

Key words: major project, collaborative management, infectious risk