Measuring walking forces of small or tiny insects can help the comprehension of their locomotion principles.How-ever,as their size and force are generally too small,walking forces of small insects in sub-mg mass have never been actually measured.In this work,a convenient multi-lens and jelly surface based shadow method was developed for simultaneous multiple walking forces measuring,ranged from nN to mN with a sensitivity of sub-nN/pixel under ambient conditions.Walking force of six legs of a 0.3 mg water treader was demonstrated.The obtained results disclosed a rapid and ex-tending middle leg strategy of water treader in walking forward above a jelly surface.This method is cost-effective and high-resolution,which could be easily used in measuring other tiny forces.