Tunnel laying is widely used in urban transmission network because of its large transmission current， easy management，maintenance and inspection． Optimizing the layout of multi-loop cables can make full use of its load capacity． In this paper，considering the electromagnetic field，thermal field，fluid field and the cross-bonding grounding mode，a simulation model of magnetic thermal flow and circuit coupling for a seven-circuit high voltage cables in a tunnel was established． The model was verified by infrared temperature measurement． Taking the induced voltage of metal sheath not exceeding the standard value as constraints and the minimizing the highest core temperature of cables as objective function，The phase sequence and position of the cable are optimized jointly based on memetic algorithm． After optimization，the maximum core temperature，sheath circulation loss，average circulation value and induced voltage of the cable decreased by 8. 18% ，21. 39% ，30. 62% and 8. 20% ，respectively． The result shows that the adoption of memetic algorithm，by properly increasing the horizontal distance of the tunnel cable loop and selecting the appropriate phase sequence layout，is conducive to weakening the mutual heat effect between the loop cables，reducing the circulating heat loss of the metal sheath，and improving the layout of the tunnel cable．