According to the actual application of a standard library cell operating in the near-threshold voltage region，and due to the problem of large error in the lookup table of traditional library files，this paper proposed a method to characterize the standard cell in near-threshold voltage region. The method redefined the boundary of the lookup table by analyzing the actual application of standard cell in near-threshold voltage，and by analyzing the relative error between the circuit synthesis result and circuit simulation result，it re-determined the scale of the lookup table，in order to improve the accuracy of standard cell library in near-threshold voltage region. This method was then used to characterize the smic55nm CMOS process library file in 0.6 V voltage and evaluate the relative error，and the results show that when compared to the library file established by traditional characterize method，the proposed method improved the library file's accuracy by 16%~63.51%，reduced the error of lookup table，and effectively improved the accuracy of library file.