This article defines and systematizes the main factors that generate the instability of the external financial environment of the enterprise. In particular, an independent group of global factors of the external financial environment of the company, which are generated by the development of the global economy as a whole, is singled out. Among the factors of this group are primarily considered those that determine the cyclical nature of financial crises. The main principles of estimation and forecasting of certain parameters of the instability of the external financial environment of the enterprise are considered, namely the standard deviation indicator, coefficient of variation, risk value, instability coefficient. The main forms of taking into account the influence of the instability of the external financial environment on the individual processes of developing the financial strategy of the enterprise are determined. Phases of the overall process of financial strategy development: diagnosis of strategic opportunities of financial development of the enterprise; development of a complex of strategic financial decisions of the enterprise; realization of the developed financial strategy of the enterprise.