The laying of multi-circuit cables with double-channel cable trench is a special installation，and there is a lack of relative researches on the influencing factors of the ampacity of such cables． In this paper，a finite element simulation model based on electromagnetic-thermal-fluid coupling was established to analyze the heat dissipation characteristics and influencing factors of the cables installed in double-channel trench，and a corresponding improved laying scheme was proposed． The results show that，under the same load，the temperature of the two circuits near the middle trench wall is more higher，and this is the bottleneck of the ampacity． The decrease in the width of the cable trench makes the temperature of the cable conductor rise linearly，and the temperature rise of the cable circuits near the middle trench wall is greater． The backfilled sand will strengthen the thermal influence of cables in double-channel，leading to a severe reduction on ampacity． And in that case，the thickness of the middle trench wall will have a great impact on the ampacity of the cables． The improved scheme proposed in this paper can significantly improve the ampacity of double-chanel cables when the backfilled sand has poor dissipation performance．