Nonstandard samples were used to conduct fatigue experiments on brittle material (PMMA) to study the effect of local state of stress at crack tip on fatigue crack propagation rate (FCPR). Results indicated that FCPR cannot be generally characterized by cyclic stress intensity factor range alone and that a second parameter representing the influence of K-dominance zone size and nonsingular stress field is needed. New phenomenological model based on the two-parameter fracture mechanics is proposed for FCPR prediction. Model allows accurate transferability of laboratory data to life prediction in service situations of defects in engineering components under fatigue conditions.