Aspect, as one of the elements of verb mechanics, has been overlooked by many language designers. This paper argues that an artificial language, designed as a universal language for international communication, should incorporate the "universal" component of aspect found cross-linguistically in natural languages. In doing so, the paper develops a two-level model of situation aspect in which situation aspect is modelled as verb classes at the lexical level and as situation types at the sentential level. With a framework consisting of a lexicon, a layered clause structure and a set of mapping rules, the model is developed and tested using an English corpus and a Chinese corpus.