Abstract: The arch dam is analyzed by the load distribution-stiffness method. The cracking section performance functions are set up according to the limit state of every combined internal force. The formula of the gradient vector of every performance function is derived, and the iterative and recurrence formulas of collapse probability of section are obtained. The reduction of the arch dam's degree of statical indeterminiacy is carried out according to the failure of the section. The cracking trajectory of arch dam is traced in accordance with the progression of cracking sections. The conditional probability vector of cracking trajectocy of arch dam is formed in terms of the progression of conditional probability of cracking section of arch dam.