A method of real-time monitoring ionosphere based on GPS technology is described in this paper. The regional ionosphere model is constructed using GPS phase-smoothed pseudorange measurements. The ionosphere delay and instrumental bias are also calculated. Because the instrumental bias is stable, its value can be obtained after a period of time. Using this value, realtime instrumental bias can be forecasted. After deducted the instrumental bias from GPS signal, the real-time ionosphere information can be extracted in path of signal propagation. To validate this method, the data of Shanghai regional GPS network are used and a real-time regional ionosphere model is created. The results show the internal precision of this regional ionosphere model are better than 3TECU.