With the gradual maturity of 5G, the mainstream band for 5G deployment is 3.5GHz, which has advantages such as 100M large bandwidth and large capacity. However, it also has characteristics such as high path loss and poor penetration, which lead to poor coverage performance. The characteristics of 2.1GHz NR are just the opposite of 3.5GHz, which can make up for the loophole of poor coverage capability in 3.5GHz band. Therefore, the current network deployment needs to combine the advantages of each of the two frequency bands and rely on Carrier Aggregation(CA) technology to improve the coverage capability of the high and low frequency cooperative network. In this paper, the theoretical analysis of high and low frequency carrier aggregation to enhance the depth coverage capability will be conducted, and the theoretical analysis will be verified by combining with the existing network test. This is an important reference for operators to deploy in this scenario.