This paper addresses key issues such as “insufficient quantification of ball stability in metal sphere systems、lack of systematic parameter constraints in ball search processes、unclear mechanisms of range-bin crossing and deviation amplification patterns.” Proposes an absolute far-field calibration scheme for weather radar that combines an equipped UAV, a laser-range-finding camera and a standard metal sphere. First, a stability metric constrained by a maximum horizontal displacement (S≥ 97%) is defined to determine the sphere’s optimal calibration position. Next, an “cross-scan” procedure is devised to locate the sphere rapidly and precisely at the antenna main-beam center and the midpoint of the chosen range bin. Finally, using the S-band dual-polarization reference radar (Z9740) at the Changsha Weather-Radar Calibration Center as a test case, results show that when the sphere is centered in the range bin, the mean deviations of reflectivity (Z) and differential reflectivity (ZDR) from their theoretical values are only -0.2 and 0.16 dB, the retrieved beamwidth, antenna gain and pulse width differ by just 0.01°、0.14 dB and -0.11 μs. If the sphere straddles adjacent range bins, the Z and ZDR errors enlarge to -4.03 and 0.45 dB, and the beamwidth、gain and pulse-width errors increase to 0.06°、-0.17 dB and 0.56 μs. Comparative tests reveal that “pulse-window overlap” is the root cause of energy splitting and bias growth, and improvement measures such as dynamic position control and pulse windowing are recommended. The approach can tighten absolute calibration accuracy of Z and ZDR to within 0.5 and 0.2 dB, providing an absolute validation method for nationwide radar-network consistency assessments.