Short term flicker severity Pst is an important index to measure the power quality in the IEC standard, and the accurate calculation of Pst is the precondition to improve power quality. In order to improve the calculation accuracy of Pst, a novel method based on atomic decomposition and the real-coded quantum evolutionary algorithm is proposed to calculate the short time flicker severity Pst. Its core is that, firstly, on the basis of the Gabor complete atomic library, the real-coded quantum evolutionary algorithm is used to optimize the atomic parameters instead of using the matching pursuits algorithms, thereby improving search efficiency. Secondly, atomic decomposition technique based on real-coded quantum evolutionary algorithms is adopted to analyze harmonic components of the voltage fluctuation signal of power systems, which improves analysis ability. Finally, the proposed method is used to calculate Pst to improve calculation accuracy. Simulation experiment shows that based on the atomic decomposition and real-coded quantum evolutionary algorithm, the calculation results of the short time flicker severity Pst for power systems have higher precision compared with the results of other methods. This proves the validity and applicability of the proposed method.