Graphical abstract Fischer-Tropsch synthesis (FTS) always exhibits Anderson-Schulz-Flory (ASF) pattern in the carbon number distribution at conventional reaction conditions, which limits the selective synthesis of desired middle distillates and wax. In our study, the addition of small amount of water into a batch slurry phase reactor gives a marked effect on the carbon number distribution so that the selectivity in the range of C 8–C 30 increases obviously along with an increase in carbon number ( n), which leads to a substantial deviation from ASF pattern (78.6% in C 11+ hydrocarbons). In contrast, in the absence of water, the carbon number distribution of FT products follows the classical Anderson-Schulz-Flory (ASF) pattern (28.3% in C 11+ hydrocarbons). The effect of water is explained by suppressing secondary hydrogenation of 1-olefins and facilitating their readsorption and chain growth. Highlights ► Fischer-Tropsch synthesis (FTS) is carried out in a batch slurry phase reactor. ► Water addition suppresses the hydrogenation of in situ 1-olefins. ► In situ 1-olefins are efficiently utilized for secondary chain growth. ► Water addition leads to a remarkable anti-ASF distribution. ► Hydrogenolysis of the FT hydrocarbons is a reversible process to FTS.