When multiple ground-based radars (GB-rads) are utilized together to resolve three-dimensional (3-D) deformations, the resolving accuracy is related with the measurement geometry constructed by these radars. This paper focuses on constrained geometry analysis to resolve 3-D deformations from three GB-rads. The geometric dilution of precision (GDOP) is utilized to evaluate 3-D deformation accuracy of a single target, and its theoretical equation is derived by building a simplified 3-D coordinate system. Then for a 3-D scene, its optimal accuracy problem is converted into determining the minimum value of an objective function with a boundary constraint. The genetic algorithm is utilized to solve this constrained optimization problem. Numerical simulations are made to validate the correctness of the theoretical analysis results.