Abstract: When cold and hot pipelines are laid in parallel, a special temperature field will be formed around the pipelinesand in their surrounding soil. The reasonable heat-transfer calculation boundary conditions during heat-transfer numericalsimulation of parallel pipelines are discussed. The results indicate that for the temperature field of buried parallel pipelines, when the computational domain is large enough, the calculation results using the first type and second type of boundaryconditions for left and right boundaries are identical, the calculation results using the first type of boundary conditions isslightly greater, that using the second type of boundary conditions is slightly smaller, and their difference is significant whenthe computational domain in the depth direction is 10 times smaller than the pipe diameter, the transverse dimension ofthe computational domain should not be 20 times smaller than the pipe diameter, and the dimension in the depth (vertical)direction should not be 10 times small than the pipe diameter. The research conclusions can provide reference to the pipelineengineering design and operation personnel to optimize their design and operation plans.