Ecological security and its patterns are hot topics for regional ecological protection. In the subtropical coast mountainous area with high precipitation, complex topography, and frequent typhoons, does the construction of a Power Transmission Line (PTL) affect local ecological security? Taking Fujian Tangyuan PTL as an example, this study examined changes in the Ecological Security Pattern (ESP) at regional and local scales by using Morphological Spatial Pattern Analysis (MSPA), Minimum Cumulative Resistance (MCR) and the Gravity model. The results showed that within the PTL timelines (before, during and after building the PTL), the ecological source area occupied 14.21%, 11.79% and 14.11% of the whole research region; while the important eco-corridors numbered 20, 21 and 16, respectively; and the eco-nodes numbered 168, 123 and 227, respectively. At the local scale, in the PTL buffer space (2 km from the PTL on either side, i.e., the potential ecological impact zone) within the timelines (before-during-after building the PTL), the ecological source area occupied 39.78 km², 27.44 km² and 29.88 km², respectively, and the eco-corridor lengths were 50.78 km, 44.36 km and 67.18 km with 13, 7 and 25 eco-nodes, respectively. Clearly, during the building of the PTL, the ecological “source-corridor” decreased at first and gradually recovered after the construction, while the challenge to the ecological safety from the PTL occurred at the local scale. The results of this study provide a method for evaluating the ecological integrity disturbance by linear projects and scientific protection strategies are proposed.