The invention discloses a tobacco shred structure determining method and device suitable for thin cigarettes. The tobacco shred structure determining method comprises the following steps: tobacco shreds of different lengths are subjected to mixing combination through a mixing uniform design method, and a plurality of tobacco shred structures are obtained; the physical index and the smoke index ofeach cigarette made of the corresponding tobacco shred structure are detected, and variable coefficients of all the indexes are calculated; all tobacco shred component proportions in the tobacco shredstructures are subjected to quadratic polynomial stepwise regression analysis, regression function models of all tobacco shred components and the variable coefficients of all the indexes are established, the regression function models are optimized, and tobacco shred length intervals and the variable coefficients corresponding to all the optimal indexes are obtained; the variable coefficients ofall the indexes are compared through combination of the Delphi method and an adjacent index comparison method to determine weights of all the indexes; and the weights of all the indexes and the variable coefficients of all the indexes are subjected to weighted average calculation, all the tobacco shred component proportions corresponding to the minimum variable coefficients of all the indexes areobtained, and the optimal tobacco shred structure is determined.