Abstract: The length of the flow recovery zone of spur dike is an important index in understanding the impact scale of spur dike groups, and there are no much research results on this at present. We convert the recovery zone length into the difference between two spacing thresholds, the first threshold is based on the cross-section velocity distribution principle of double spur dikes(criterion II) and the second one is obtained by large-scale vortexes nonoverlapping principle(criterion I). Through RNG k-ε turbulence mathematical model after calibrating and numerical simulation test, we establish the empirical formula of spacing threshold of criterion I. The empirical formula for calculating the length of the flow recovery zone of nonsubmerged spur dikes with alternate layout is obtained based on the empirical formula of spacing threshold under criterion II and I. The verification results of the formula show that the calculation accuracy is satisfactory and has certain value-in-use, which will provide a reference for the reasonable arrangement of the spur dike groups in the river system.