Being restricted by the environment and according to the urban planning, some HV cables have to be laid under the existing buildings or pipelines, the values taking for safety distance should be calculated in the trajectory design. In this paper, a case of directional drilling project is discussed, which is 110kV HV transmission cable line in Xiamen. According to the existing technical codes in China and based on the engineering cases investigation, the analysis was made on the influencing factors on the safety distance value taking for electric power cable protection pipe laying to optimize the pipe laying trajectory. Xiamen 110kV HV cable protective pipes have been laid successfully under the ground, which can provide references for similar construction.