The habit of cadmium mercury thiocyanate (CMTC) crystal for laser diode frequency doubling when crystallized from KCl-H2O solutions at 28 degreesC under different conditions was investigated by means of a micro-crystallization method. The results show that CMTC crystals exhibit a regular crystalline morphology, homogenous growth rate in different directions and are transparent when the concentration of KCl ranges from 3% to 10% and pH from 3.0 to 4.0. Decrease in pH value leads to an increase in the crystallization rate along the c-axis direction, and a decrease along the a-axis direction. Impurities greatly affect the crystalline quality and morphology of the crystal. With aging and increasing temperature the solution becomes unstable. In this paper, suitable conditions and key factors for CMTC crystal growth are discussed.