This paper reports on an algorithm for hourly simulation of ground-coupled heat pump (GCHP) systems. This algorithm integrates the newest analytical models for COP of heat pumps and for heat transfer of ground heat exchangers (GHEs). These analytical models make the algorithm computationally fast and efficient. The algorithm comprises 7 independent equations for solving 7 system variables, thus including C-14(7) = 3432 simulation scenarios. The algorithm is applied to hourly 50-year simulations of a GCHP for illustrating the computation efficiency of the algorithm. The simulation cases show that the COP and seasonal COP of GCHPs depend heavily on the mutual-cause coupling between the ground-side load and the temperature field in the ground. This coupling effect renders the high-resolution simulation highly necessary.