Indoor positioning is not a popular technology, although it is widely used in our daily life. In order to achieve accurate positioning in the indoor complex environment, a light, convenient and offline WiFi positioning system is designed. The system based on Android platform is developed, which is based on the improved RSSI algorithm added by after verification method to avoid the excessive migration of the position coordinates. Compared with the conventional WiFi positioning system, the database of the system is integrated in the equipment to avoid the positioning delay and failure caused by the connection of the database and the communication inconvenience. After testing, the system can work stably and control the range of error within 3 meters in the corridor room scene, which can meet the requirement of indoor mobile positioning.