Currently, more and more application-specific operating systems (ASOSs) are applied in the domain of real-time embedded systems (RTESs). With the development of a microkernel technique, the ASOS is usually customized based on a microkernel using the configurable policy. Evaluating the timing requirements of an RTES based on the ASOS is helpful to guide the designer toward the choice of the most appropriate configuration. Modeling and analyzing the time requirements for such a system in the early design stage are essential to avoid redesigning or recoding the system at a later stage. However, the existing works are insufficient to support the modeling for both the specific domain of the microkernel-based RTES and the variability of the configurable policy, as well as a general analysis for the various configurations. To solve these problems, this paper presents a modeling and timing analysis framework (MTAF) for the microkernel-based RTES. Our main contributions are twofold: 1) proposing a domain-specific language (DSL) for the timing analysis modeling of the microkernel-based RTES; then, we define and implement this DSL as a UML profile and (2) proposing a static timing analysis approach for the RTES design modeled by the DSL, where a timing analysis tree and uniform execution rules are defined to analyze the variability in a general way. In the case study, we take the scheduling policy as an example to show the use of our framework on a real-life robot controller system.