A method of evaluating strength of root lodging resistance in maize stalk was developed. It constructed a mechanical model of cantilever beam to describe maize stalk. The maximum vertical root-pulling resistance was used as a measurand for evaluating the strength of root lodging resistance in maize stalk. A measuring instrument was designed which consisted of a screw mechanism, an activities tripod platform, a gripper and measurement parts. Force which was transferred to the screw mechanism with the help of a hand wheel was only 1/97 of the maximum vertical root pulling resistance. The gripper with two different devices could clamp most of the maize stalks with different diameters. Field experiments showed a significant negative correlation existed between maximum vertical root-pulling resistance and root lodging.