Data gathering by the sensor is most important task in Wireless Sensor Net-works (WSN) application like healthcare and security. In that to provide a Quality of Service (QoS) is major challenges due to processing a non-important packet prior to the import or critical packet. So that performance of the node is reduced and critical data is affected in the application. In this paper a priority based mathematical model is used to attain the QoS by assigning a various priority level for incoming packets. High level priority is given to the most critical data, least priority for Ordinary packets. So that the Critical data will be processed soon for data sensitive application. © Research India Publications.