An experimental study on the energy conversion process of a continuous wave (CW) laser thruster is presented. The effect of the flow parameters on two dominant loss mechanisms of a CW laser thruster was investigated by using a CW CO2 laser with output power of 700W. The laser transmission and radiation from the laser sustained-plasma (LSP) were measured for several flow velocities and pressures, which were independently controlled. CCD camera was employed in order to observe the shape and position of the LSPs. We found that the energy conversion process is optimized when the LSP is in the vicinity of the focal point of the condensing laser beam.