Based on IEEE 802.15.4, the contention-free period (CFP) adopts a guarantee time slot (GTS) mechanism to ensure each device can access the radio channel. However, it is hard to get the authority to access the radio channel due to more competitor access the radio channel simultaneously. To cope with this issue, we proposed a guarantee time slot mechanism to enhance the performance and utilization by using CFP. Our proposed method ensures each device has the authority to access the radio channel without any additional step. By comparing with the method of IEEE 802.15.4, the experimental results show that data average transmission delay and energy consumption can be reduced dramatically. In addition, the bandwidth and performance of network is improved since the pre-allocation mechanism can reduce the number of control packets. Several experiments have been conducted to demonstrate the performance of our work.