In this paper we report the experimental results of controlling CuBr laser modes by using an injection seeding technique. We have amplified the single longitudinal mode CuBr laser pulses and obtained the narrowing-linewidth copper laser radiation with an average power of more than 100 mW. Theoretically, we have analysed the injection seeding process in short-pulse high-gain lasers and discussed the experimental results in the injection seeded CuBr laser.