As an important Light Emitting Diode(LED) substrate material, GaAs single crystal has been widely used in optoelectronic devices, but the defects such as uneven distribution of carrier concentration (C.C.) and high concentration of impurities seriously affect the performance of corresponding devices. In order to prepare a Si-doped HB-GaAs single crystal with uniform longitudinal distribution of C.C., the influence of the melting zone length on the longitudinal distribution of C.C. during crystal growth was investigated. Using high-purity GaAs polycrystals as raw materials, setting different crystal pull temperature curves, and using narrow-melt zone technique for the crystal growth research, finally, N-type Si-doped <111> GaAs single crystal having a more uniform distribution of C.C. and lower dislocation density (EPD≤10 000 cm-2) was obtained. The crystal was characterized by glow discharge mass spectrometry (GDMS) and Vanderbilt method. The purity of the single crystal reaches 5N which stained without boron impurities.