Abstract: In order to improve the efficiency of high intensity focused ultrasound (HIFU) therapy, lesion formation induced by HIFU in continuous scanning mode along a spiral scanning pathway were theoretically and experimentally investigated in the present work. The Khokhlov Zabolotskaya-Kuznetsov equation and bio-heat equation were combined in the current model to predict HIFU-induced temperature distribution and lesion formation. The shape of lesion and treatment efficiency were assessed for a given scanning speed at two different grid spacing (3 mm and 4 mm) in the gel phantom study. The results show that uniform lesions can be generated by the homogenization of thermal diffusion along the spiral scanning pathway. On this basis, the complete coverage of the entire treated volume can be achieved and treatment efficiency can be optimized by choosing appropriate grid spacing and scanning speed. This study is helpful for further optimization of HIFU therapy.