Abstract: To survey the development of expert system，this paper partitions expert systems as 5 stages： rule-based，
frame-based，case-based，ontology-based，and web-based，on the basis of development sequence.In each stage the concept of
corresponding expert system is analyzed，the typical algorithm is put forward，and some representative examples are advanced. Then，the development law is proposed，which is advised to consist of principle development law and technique development
law.The principle development obeys the negation of negation law while the technique development can be seen as the interdisciplinary.
In the end，the further direction of research is predicted.