The invention discloses online radiotherapy plan quality control software which comprises a DVH prewarning value template setting interface, a data read-in interface, a radiotherapy plan DVH prewarning value setting interface, a sketching and integration interface, a plant evaluation interface, an online adjustment interface, an image deformation registration algorithm, an online plan modification algorithm and a dosage calculation algorithm. A fusion image is generated through an original image and an online image, a target section is described, the endangered organ profile is subjected to online sketching, based on this, dosage calculation is conducted, DVH is generated, comparison with the DVH prewarning value set by a doctor is conducted, online evaluation and adjustment of a radiotherapy plan are achieved, and precise application of the radiotherapy plan is guaranteed.