Numerous studies of DC and rf systems have found that the achievable surface field is strongly dependent on the global parameters of a system, such as the gap between electrodes, rf frequency, group velocity for TW, Q for SW, and number of cells of an accelerating structure. However there is very little understanding of the physics behind these dependences. Generally, field emission is considered the fundamental trig for breakdown. In fact we found there is strong dependence of dark current on rf net power flow or stored energy in an rf cavity in recent experiments. Meanwhile, a theoretical model is being built to study the effect of macroscopic geometry on microscopic field emission. In simulation we found that electron emission from metal surfaces in a high field environment generates local electric fields that can enhance the emission. This enhancement dependences on the rf frequency, and in the case of a waveguide, the group velocity. This phenomenon may explain the observed dependence of breakdown rates on the rf characteristics of the structures, in particular, those relating to rf power flow. In the talk, I’ll review a series of experiments that have been done in past few years for breakdown and discuss the undergoing experiment and theoretical of model of field emission coupled with macroscopic parameters.