In order to investigate the intrinsic mechanism of sucrose participated in drought tolerance in plants, the study used the phosphoenolpyruvate carboxylase (C₄pepc) transgenic rice (Hereinafter referred to as PC) and untransformed wildtype “Kitaake” (Hereinafter referred to as WT) rice lines. PC and WT were treated with different concentrations of sucrose during seed germination under simulated drought treatment (10% PEG6000). The performance of seed germination, total soluble sugar and sugar components contents, total soluble protein content, transcript levels of genes of sucrose nonfermenting1(SNF1)related protein kinases (SnRKs) and transcript levels of PEPC genes in rice lines were measured. The results showed as following: (1) external application of sucrose solution showed the similar effect with the seed germination of rice, but significantly promoted the seed germination with low concentration of sucrose solution companying with drought treatment. External application of sucrose solution showed a concentrationdependent effect on seed germination of two rice lines. High sucrose concentration (>150 mmol·L^-1) further inhibited drought effect, while low concentration (<30 mmol·L^-1) alleviated drought inhibition. However, the sensitive concentration of sucrose with the best effect on seed germination was different in two lines under drought treatment, PC (<6 mmol·L^-1) is much lower than WT (<30 mmol·L^-1). And this performance is consistent with the dynamic changes of the activity of αamylase in two lines as well. (2) Compared with WT, 3 mmol·L^-1 sucrose combined with drought treatment significantly promoted the performance of seed germination in PC with a significant increase of endogenous sucrose content, total soluble sugar content and soluble protein content. Furthermore, the treatment of 3 mmol·L^-1 sucrose with drought significantly decreased the transcript level of C₃pepc, but significantly increased C₄pepc in the PC, respectively (P<0.05); (3) Some sugar signaling related genes such as SnRKs family genes including SnRK1s (OsK1a OsK24 OsK35) and SnRK2s (SAPK6) in PC rice also significantly increased their transcript levels after the same treatment as above. The results showed that PC can increase the contents of soluble sugar and soluble protein, regulate the expression of SnRKs subfamily genes and exogenous C₄pepc by increasing low sucrose, improve the activity of αamylase, and therefore alleviate the inhibitory effect on the seed germination under drought treatment.