Compared to open water, the presence of ice floes in ice-covered water may pose additional challenges tothe towing operations of offshore platforms. This paper proposes a numerical model for analyzing coursestability of a gravity-based structure during towing operation in managed ice fields, considering coupledmotions of tugs, towed platform, and ice floes. A discrete element method is applied to simulateinteraction between drifting ice floes and structures, and verified by existing model tests. The motions oftug and towed platform are coupled through a catenary towline model. A proportional-differentialcontroller is employed to adjust heading and lateral position of tug. The effects of main factors, such astugs’ number, towline length, ice concentration, rudder area and controller gains on course stability arediscussed through numerical case studies. The presented numerical approach is expected to providepractical guidance for towing design, and ensure safety of towing operation.