The government investment in the construction project general always use of the design budgetary estimate as the construction-agent charge fees foundation, and with reference to the owners management cost rate to calculate the construction-agent charge. By analyzing the composition of the construction agent charge and the difference between the owners management cost and the construction agent charge, studying of the composition and rates of construction-agent charge in various key cities nationwide in detail, pointing out the fact that the current generation of construction-agent charge rates are too low, and then established a system dynamics model and analyzed the relationship between a reasonable profit margins and project success rate dynamically. Pointed out the necessity of a reasonable profit margin, and make same recommendations accordingly.