Quality of the software is considered as an integrated criterion consisted of the numeric and qualitative characteristics defined by the standards of the various level: ISO, national standards, standards of the companies, and project’s standards. It is shown that the software quality planning during various stages of development can be realized by using the system dynamics method that is suggested as a formal method of the quality management. The examples of the equations used for software quality characteristics variation that depend on the changing of external factors, such as complexity of development, experience of software developers, experience of operating personnel, currency exchange rate, business reputation of the software developers, and business reputation of the company, in which the software is operated, are given. The solution example for the system of dynamics equations used for the planning of the software quality is described as well.