Unified programming models can effectively improve program portability on various heterogeneous high-performance computers. Existing unified programming models put a lot of effort to code portability but are still far from achieving good performance portability. In this paper, we present a preliminary design of a performance-portable unified programming model including four aspects: programming language, programming abstraction, compilation optimization, and scheduling system. Specifically, domain-specific languages introduce domain knowledge to decouple the optimizations for different applications and architectures. The unified programming abstraction unifies the common features of different architectures to support common optimizations. Multi-level compilation optimization enables comprehensive performance optimization based on multi-level intermediate representations. Resource-aware lightweight runtime scheduling system improves the resource utilization of heterogeneous computers. This is a perspective paper to show our viewpoints on programming models for emerging heterogeneous systems.