The invention discloses an image-guided ablation surgery planning device, which comprises a patient three-dimensional image construction unit, an image display unit, a surgical path input unit, a microwave energy field computing unit, a temperature field computing unit, and a damage field computing unit, wherein the patient three-dimensional image construction unit is used for acquiring a three-dimensional image of the patient according to the CT or MRI medical image of the patient; the image display unit is used for displaying the three-dimensional image of the patient; the surgical path input unit is used for inputting needle inlet point, angle, depth, power and ablation duration of the ablation surgery; the microwave energy field computing unit is used for computing the distribution of microwave energy absorbed by tissues to be ablated in unit time and unit volume; the temperature field computing unit is used for computing the temperature field distribution of the tissues to be ablated by taking the computed microwave energy field as an internal heat source; the damage field computing unit is used for computing temperature damage areas of the tissues to be ablated; and the computed temperature damage areas are displayed on the three-dimensional image of the patient in a fusing way through the image display unit. The device can reflect the true anatomical structures of organisms and tumors in a mode of the three-dimensional image and predict an ablation range accurately so as to provide objective reference for implementing the ablation surgery.