A reasonable definition for a solid state reaction is presented. And the position in synthetic chemistry for a solid state reaction at high, moderate, low-heating temperatures is described, respectively. The characteristics and the potential applications of a solid state reaction at low-heating temperatures to synthetic chemistry, especially in the syntheses of nanocrystals and non-linear optical materials, are emphasized. Some typical examples in chemical industry are illustrated to show that the application of the solid state reaction at low-heating temperatures should be developed in the future chemical industry due to its advantages of conserving energy, achieving good yield, being absent of solvent, and producing almost no pollution.