The effects of whole purple sweet potato flour (WPSPF) addition on the processing characteristics of plain flour (PF) and the effects on the eating quality of steamed buns made from WPSPF-PF composite flours was analyzed. The results indicated that adding WPSPF increases the moisture retention while decreasing the oil retention. Thermodynamic analysis indicated two gelatinization peaks for the WPSPF-PF composite flours. Pure WPSPF has higher gelatinization onset (To), peak (Tp), and end (Tc) temperatures than pure PF, but has a lower ΔH. Composite PF showed To, Tp, and Tc temperatures between 60.67 ℃ and 71.43 ℃, which are considerably higher than those of pure PF, and ΔH of 0.49~1.21 J/g, which is slightly lower than that of pure PF. The To, Tp, Tc, and ΔH values of 78.33~87.97 ℃ and 0.06~ 0.38 J/g obtained for composite WPSPF are all lower than those of pure WPPF. The ability of the dough to form gluten networks decreased as the percentage of WPSPF in the composite flour increased, reducing the formation and stabilization times. Consequently, WPSPF addition increased the hardness, viscosity, and chewiness of the steamed buns, while decreasing their recovery, elasticity, cohesiveness, and stickiness. WPPF also increased the resistant starch content of the steamed buns by 1.77~11.47 g/100 g as compared to the control group. Steamed buns with 10%~30 % WPSPF were found to be highly acceptable in terms of color and sensory quality. The findings of this study are expected to serve as a reference for the development and utilization of WPSPF.