In the case of limited mobile device performance, a Two-channel Dynamic Encryption Strategy (TDES) based on greedy algorithm was proposed to perform selective encryption to the data packet, so as to maximize the total privacy weight of packets in a limited time. First, the data packets were roughly classified into two categories according to the privacy weight of the data packets. Then, the weight ranking table was calculated by the privacy weight and the encryption time of the different data packets and sorted in descending order.The two types of data packets corresponded to two transmission channels, and the packet with the maximum privacy weight was encrypted for transmission until at the end of the transmission time. Finally, the remaining time inside the channel was checked, and the transmission channels of some packets were adjusted until the remaining time was less than the encryption time of any packet. The simulation of packet transmission tests shows that compared with Dynamic Data Encryption Strategy (D2ES) and greedy algorithm under the same time limit, the total privacy weight of the proposed strategy was increased by 9.5% and 10.3%, and the running time of the proposed strategy was reduced by 10.8% and 8.5%. Experimental results verify that the proposed TDES has shorter computation time and higher efficiency, which can well balance data security and equipment performance.