External environment shapes the cold adaptation of Ophraella communa, a specialist natural enemy of the invasive common ragweed, and further affects its biological control efficacy. Our study aims to clarify the cold tolerance correlation between ragweed and leaf beetle and explore whether host cold acclimation can enhance the beetle’s low-temperature adaptability. We measured cold-resistant substances, supercooling point (SCP), and chill-coma recovery time (CCRT) of four geographic populations, and conducted indoor low-temperature acclimation of ragweed at 13 °C, 17 °C, 21 °C for 3–9 d, then fed leaf beetle with treated leaves. Results showed that cold-resistant substances in both species varied with latitude and were highly heritable. Cold acclimation can elevate sugars, trehalose, glycerol, and proline in ragweed; the cold tolerance of beetles feeding on these plants was significantly improved. We conclude that cold-resistant substances in ragweed can be trophically transferred to leaf beetle to enhance its cold hardiness, providing a new strategy to improve biocontrol in high-latitude regions.