This paper reports the estimation carried out of the state influence of a disk work surface upon output indices of external circular grinding. There are offered dependences for the computation of a mathematical expectation, correlation function and dispersion of a current radius-vector. The analysis of influence of a profile random component upon a process dynamics is carried out. The examples of spectrum characteristics of a random component of a tool profile deviations, a square of module frequency characteristics of the system and power spectrum of tool center oscillations caused by random deviations in an abrasive disk profile are shown. The interrelations established allow forecasting the behavior of an external round grinding, computing corrective control impacts, and carrying out a billet surface effective working taking into account conditions changed. The outlooks for the further development of results obtained consist in their application for the choice of project solutions, the characteristics evaluation of technological grinding systems and grinding optimization at billet working on the automated equipment.