Abstract: The aligned grid sampling pattern is one of the most convenient sampling methods in precision agriculture. The objective of this research is to use computer simulation to determine the optimal sampling density for the aligned grid soil sampling pattern to balance the cost and precision requirements in precision agriculture applications. A mathematical diffusion model was constructed, and 2～4 diffusion seeds were set in a 100×100 grid with a grid cell size of 1×1 unit to diffuse and accumulate point values according to the diffusion model. The diffusion results could well simulate the distribution of some attributes in the field. The computer simulated sampling points with different grid cell sizes were generated and then interpolated into 10000 points with inverse distance weighted(IDW). Finally, the original value was compared with the interpolated value for the same grid cell to find the sampling error, and optimal sampling points were determined according to the allowable sampling error. Test results showed that if the sampling grid cell sizes were about 11 times and 17 times the output cell size of the attribute map, the average relative sampling errors could be limited to 10% and 15%, respectively. The optimal density of sampling points can be determined by the sampling grid cell size and the field area.