This paper presents a general object-oriented model for measurement systems. The limitations of the conventional function-oriented models are examined in the light of the generalised concept of measurement and its theoretical framework proposed previously by the author. The proposed model identifies five classes of objects, i.e. measured object, measuring instrument, reference standard, human observer and operating environment. Each of them is characterised by its own attributes and operations or functions at three levels, i.e. internal, operational and environmental. The interactions between them are also modelled including the coupling between the measured object and the measuring instrument, the human-instrument interface, the calibration and the interference. Together with the generalised concept of measurement and its philosophical framework, it serves as a practical tool for description, analysis and design, and, in particular, for computer aided analysis and design of a measuring system. It will find applications in instrumentation engineering and measurement education and research.