[Objectives]  To determine the optimal morphological characteristics for identifying nymphal instars of the yellow-spined bamboo locust, Ceracris kiangsu (Orthoptera: Arcypteridae), examine the applicability of Dyar and Crosby rules to this species, and provide a theoretical basis for determining the nymphal instars of Orthopterans based on the variability of morphological characteristics of different developmental stages. [Methods]  Nymphs were reared in an insectary after hatching. Eight morphological variables, including body length, body weight, head length, head width, wing bud length, wing bud width, wing bud area and antennal length, were measured and analyzed statistically for each instar. [Results]  Five instars were distinguished without gender differences. Five distribution peaks were apparent based on head length and head width, and three concentrated distribution areas for wing bud width and wing bud area were apparent after frequency analysis. The Brooks’s ratio ranged from 1.09 to 3.86, and decreased with increasing instar. The Crosby’s ratio was over 0.1. The growth dynamics of morphological variables were not consistent with Dyar and Crosby rules. The relationship between nymph instars and the eight measured morphological variables closely approximated a polynomial regression. The linear coefficient of determination of head width had the maximum value R² = 0.933 5, and the quadratic and cubic coefficients of determination of wing bud length had the maximum value R² = 0.978 9. [Conclusion]  Head width is the optimal variable for distinguishing the nymphal instars of C. kiangsu, followed by head length and body length. All three variables can be used in pest monitoring and control.