Abstract: Action and action reasoning is a basic part of human activities. People must execute some actions when they want to complete some tasks. Similarly, robot needs to execute some actions when she accomplishes a task. High-level intelligent robot is required to be able to sense the external environment and do correct reasoning about actions independently. It is needed that the external designer writes out background axioms, sensing results and related knowledge changes for agent when expressing action reasoning with sensing actions and knowledge in situation calculus action theory. This is a kind of action reasoning depending on the designer. The situation calculus action theory is expanded in proper way, the sensors representation is added into the formal language of action theory, and agent’s new knowledge producing is based on the results of sensor applications in this paper. A platform is provided in which the following issues can be expressed formally: robot is sensing its external environment; the information obtained by robot’s sensors is converted to robot’s knowledge automatically; robot does an action reasoning independent of designer. In this way, the “black box” process of sensing actions will be clear; robot’s knowledge will be linked to the results of sensors; knowledge-fluent will be regarded as a dynamic knowledge base; and robot can update the knowledge base by executing sensing actions. Furthermore, robot can make action planning and execute actions independent of designer.