Nowadays, gas turbines (GTs) are increasingly used in China, with a relatively low performance. Organic Rankine cycle (ORC) is promising to recover the flue gas heat recovery from GT. To efficiently enhance the heat recovery, two-stage series evaporation is combined with non-isothermal phase change of non-azeotropic mixtures. Thus, two-stage series organic Rankine cycle (TSORC) with six non-azeotropic mixtures, composed of R245fa and hydrocarbons, as the working fluids are investigated. The cycle performances of TSORC with nonazeotropic mixtures are compared with those of the ORC with pure working fluid. Moreover, a case study was conducted to illustrate the performance enhancement by TSORC with the non-azeotropic mixture for fuel gas waste heat from C200HP. The results show that the net power output, thermal and exergy efficiencies of the TSORC are superior to those of the ORC at the same mass fraction, especially for the net power output. Comparing with the stand-alone gas turbine of C200HP, the TSORC with cyclohexane/R245fa[0.8/0.2] increases the efficiency of C200HP system by 35.48%, and the power generation efficiency of the C200HP-TSORC system achieves 44.71%. The TSORC with non-azeotropic mixtures as the working fluids is advisable and can be popularized in engineering applications.