Energy consumption problem in wireless sensor networks for data collection has always been a research focus. In this paper, we focus on exploring protocol of designing the constrained trajectory of the mobile sink for data collection. A universal system model for designing constrained trajectory in wireless sensor networks is firstly presented, which is formulated as the problem of the maximum total length reduction for constrained trajectory (MTRC). MTRC is proved to be the problem of NP-hard. Secondly, a greedy algorithm of trajectory constraint of low energy consumption (TCLEC) is designed and the movement trajectory of the mobile sink by maximizing the efficient length reduction is designed through TSP approximate algorithm. Theoretical analysis and simulation results show that the TCLEC algorithm has achieved high computation efficiency in the initialization and optimization of data collection tree of network topology. Compared with other hierarchical data collection methods based on mobile sink, the energy consumption has reduced about 7%.