Nowadays, low latency has become one of the primary goals of congestion control in data center networks. To achieve low latency, many congestion control algorithms have been proposed, wherein DX is the first latency-based one. Specifically, DX tackles the accurate latency measurement problem, reduces the flow completion time and outperforms the de facto DCTCP algorithm significantly in term of median queueing delay. Although the advantages of DX have been confirmed by experimental results, the behaviors of DX have not been fully revealed. Accordingly, some drawbacks of DX under special environment are unexplored. Therefore, in this paper, we conduct fluid-flow analysis over DX, deducing sufficient condition for the stability of DX and revealing the behaviors of DX. Analytical results uncover two problems of DX: (1) it has poor throughput when either the base RTT is very large or the number of flows is relatively small; (2) it suffers from large queueing delay when either the base RTT is relatively small or the number of flows is very large. These results are instructive to the improvement and deployment of DX. Simulation results based on NS-3 verify our analytical results.