Error propagation is a basic problem in analyzing uncertainty of reliable systems. During software development and dependability testing, it would be helpful to have a framework that clearly demonstrates the error propagation and containment capabilities of the different software components. However, in the former study, only the propagation characteristic of data errors in signals is considered, not including the error-generating properties of software itself induced by environment. In this paper, another error propagation frame is proposed, which not only includes the error propagation process, but also involves the error-generating ability of software itself. And this frame may be used in the later period of software development or in the process of software dependability testing. In this frame, the error propagation process in software is studied and characterized and a set of metrics that quantitatively represent the inter-modular software interactions are derived. Furthermore, a real embedded target system used in a navigation-pose control system of a satellite is used to perform fault-injection experiments to obtain experimental values for the metrics proposed. The result shows that the derived analytical framework establishes a very close correlation between the analytical and experimental values obtained. The intent is to use this framework to be able to systematically identify potential vulnerabilities in software.