There are large number of intermittently jointed cracks in rockmass, which exist in rockmass as a kind of initial damage. It is their damage, propagation and propagating interaction that result in a variety of failure forms of rockmass. This paper conducts an in depth research on the influence of cracks propagation interaction upon fracture strength of jointed rockmass. A kind of fracture strength model for jointed rockmass is developed under three-dimensional stress conditions. With the utilization of this model in a large-scale highway slope project, the design and construction are effectively performed and remarkable economic benefit has been achieved.