Application of static synchronous series compensator（SSSC） results in impacts on the measured impedance of distance protection， which will cause under-reaching or over-reaching of the distance protection. The improved wavelet packet entropy is used to analyze the transient fault current in the protection location of the series compensated transmission line with SSSC. The results show that the values of wavelet packet entropy are obviously different between fault points located before SSSC and behind SSSC. The value of wavelet packet entropy with fault point before SSSC is much larger than that with fault point behind SSSC. According to abovementioned characteristic， the identifying criterion of fault position for series compensated lines with SSSC is put forward， and based on the criterion an adjusted scheme for measured impedance of distance protection is proposed. When the value of wavelet packet entropy at the protection location is smaller than the setting value of wavelet packet entropy， and the fault point is behind SSSC， the actual fault impedance should be the original measured impedance minus additional impedance. On the contrary， the actual impedance is just the same as measured impedance. Simulation results verify the correctness and feasibility of the method proposed.