Based on analyzing risk factors of diversion project, synthetic risk rate and engineering insurance period, the frequency and distribution law of loss were researched on the grounds that foundation pit is submerged after diversion project ceases to be effective. And then, the standpoint that these total losses are subject to non homogeneous compound Poisson process is put forward. Furthermore, the collective risk model of the total losses about engineering insurance is established on the basis of construction diversion project risk. Ultimately, insurance ratemaking method for construction engineering risk and its mathematical expression is presented, which provides theoretical method for the insurance ratemaking of hydropower engineering to some extent.