Knowledge representation plays a very important role for designing knowledge base systems as well as intelligent systems. Nowadays, there are many effective methods for representing such as: semantic network, rule-base systems, computational network. Computational Objects Knowledge Base (COKB) can be used to represent the total knowledge and design the knowledge base of systems. In fact, a popular form of knowledge domain is knowledge about operations and computational relations, especially computational knowledge domain, such as: Linear Algebra, Analytic Geometry. However, COKB model and the other models have not solved yet some problems about operators: specification of operator, properties of operator, reducing an expression. In this paper, we will present a reducing model of COKB. This model, called Ops-model, represents knowledge about operators between objects and solve some problems related to these operators. Through that, the algorithms for designing inference engine of model have been built up. Moreover, Ops-model has been applied to specify a part of knowledge domain about Direct Current (DC) Electrical Circuits and construct a program for solving some problems on this knowledge domain.