Aim :To observe the qualitative changes in phantom s after they were heated by microwave atennas for hypertherm ia and to confirm the fundamental of the length of m icrowave atennas for hypertherm ia and the depth of microwave atennas inserting tissue in treatm ent.Methods: Different length of microwave atennas for hypertherm ia were inserted respectively into phantoms which are m ake up of cuboid lettuce.To measure the ranges of the qualitative changes in phantoms in the same heated time.Results: When the depth of microwave atennas inserting phantom is two times the length of antenna,the axes length of the qualitative change in the phantom is longer and the vertical length of the qualitative change in the phantom is smaller along with the length of the antenna increases.To equalength’s antennas,it is same as the form er when the depth of microwave atennas inserting increases. Conclusion:The length of microwave antennas for hyperthermia to treatment should be la≥ 1. 5 cm. The depth of microwave atennas inserting tissue in treatment should be d≥ 3cm. The changes of the length of m icrowave atennas and the depth of microwave atennas inserting can reform the patter of the qualitative change in the
