The principle and recent progress of the Terahertz Quantum-Cascade Lasers(QCL) are briefly introduced. The beam quality of different THz QCLs is studied. Beam patterns of continuous wave and pulse modes emitting devices are characterized by employing thermal detector arrays and THz Quantum-Well Photodetector(THz QWP), respectively. The detecting abilities of different arrays are compared and analyzed, and the differences in THz light characterizing between the array and THz camera are also compared. According to the results of the beam improvements, some methods of beam improvement for THz light from the THz QCL are put forward. The germanium(Ge) lens, silicon hyper hemisphere(high resistance) lens and polythene lens are good tools for improving the beam quality of THz QCLs except for employing fine waveguide fabrication process.