RFID system is a wireless technology that can transfer data between tags and readers via radio frequency. In an RFID network, readers are located close to each other to obtain optimal connectivity and sufficient coverage. In such an environment, which is called dense reader environment (DRE).Different types of collisions such as Reader-to-Reader and Reader-to-Tag ones, often lead to serious problems such as decreasing the performance. Accordingly, providing an appropriate method to resolve reader collision appeared to be one of the most important research topics in the field. To solve this problem, different methods have been introduced of which NFRA protocol has higher throughput. In this paper, we use multi-channel technique and SIFT distribution function on the NFRA protocol to improve RFID system throughput while avoiding increase in reader collision. In addition of supporting mobile reader, the proposed method provides higher throughput compared to other protocols in dense environments.