The leaf disc method is widely used in laboratory studies of the pea aphid, Acyrthosiphon pisum (Harris) (Hemiptera: Aphididae). We examined the effects of the orientation of the leaf discs (upright, inverted, and horizontally perpendicular to the surface) on the biological parameters of aphids from three populations (i.e., Gansu red, Gansu green, and Yunnan green) of A. pisum. We found that aphids feeding on inverted or horizontally perpendicular positioned leaf discs exhibited higher survival and fecundity rates than those aphids feeding on upright positioned leaf discs for all three populations. Overall, aphids in both the Gansu red and Gansu green populations performed best when feeding on the inverted leaf discs, whereas aphids of the Yunnan green population performed best in the horizontally perpendicular orientation. We postulate this may be related to body temperature adjustment by the aphids through adjusting the orientation angle between its body and the sun. Our results provide a theoretical basis for optimizing the rearing parameters of the pea aphid, reducing the systematic error of experiments, and facilitating the acquisition of more reliable data under laboratory conditions.