Performance characterization of chaotic masking encoding and decoding is studied in synchronization injected semiconductor lasers under condition of injected-feedback. The modulation response function of chaotic masking encoding and its response factor are theoretically deduced and analysed by small-signal analysis. It is numerically demonstrated that there are peak values between 1.52 GHz and 3.18 GHz when the injection coefficient is between0.2 and 0.8. The chaotic synchronization error equation is theoretically deduced and its root is given by smallsignal analysis under condition of chaotic masking encoding. The chaotic decoding formula is also theoretically demonstrated. There are the least dale values of synchronization errors between the modulation frequencies of 0.79GHz and 1.91 GHz when the injection coefficient is between 0.1 and 0.8 in numerical simulation. The numerical result is well consistent with the theoretical demonstration.