The interactions between coherent Cu precipitates with different sizes (0.5—2.5 nm) and a \begin{array}{c}\frac{1}{2}\end{array} (111){110} edge dislocation in α-Fe matrix have been investigated by molecular dynamics method (MD). Moreover, the impacts of temperatures (100—600 K) and different interaction positions for the interaction of precipitates and dislocations have been further explored. It is found that the increase of precipitates size enhances obstacle strength for dislocation glide. The reason is that the increase of precipitates diameter will increase the intercept area when dislocations pass through precipitates of different sizes. However, the rise of temperature causes the reducing of obstacle strength. By comparison, increasing precipitates diameters from 1.0 nm to 2.0 nm, critical shear stress of systems under different temperature rise by an average of 0.096 Gb/L. And when the temperature is increased from 100 K to 600 K, the critical shear stress of systems containing Cu precipitates with diameters of 1—2 nm reduces by an average of 0.049 Gb/L. The results qualitatively indicate that the effect of precipitates size plays a more important role in obstacle strength of precipitates for dislocation glide than temperature. When dislocation passes through precipitates at different sites, the precipitate whose center plane is on the dislocation glide plane is found to be the strongest obstacle. When the glide plane is the same vertically far away from the center plane of precipitates, the precipitates whose center planes are below the glide planes are stronger obstacles than those above the glide planes. The bigger contribution from the interaction between the tensile stress field below the dislocation glide plane and compressive stress field of Cu precipitate resultes in stronger hindrance for the dislocation movement.