In Robot-Soccer games, the intelligent referee system which is used to replace the human referee can perfectly simulate the thinking of human being. This paper presents an intelligent referee system, where we employ the conditional event algebra theory to make intelligent decision. In our system, we first estimate the single purpose of robots and overall purpose by searching the maximal probability of scheduled rules. Then we estimate the overall situation by calculating the favorable value according to the position and direction of ball, the home robots and the opponent robots. Combining the single and overall purpose with the field situation, we give the final results. In the experiments, the intelligent referee system based on conditional event algebra outputs satisfactory results.