Abstract: We first introduce three effects arising from the interaction of electromagnetic fields with molecules, as well as the basic principle of manipulating cold molecules using external fields, including the deceleration of molecular beams using electromagnetic fields. Various deceleration methods for molecular beams involving electrostatic Stark deceleration, magnetostatic Zeeman deceleration and optical Stark deceleration will be given, together with the experimental results and recent research progress. Finally, we will briefly present the applications of cold molecules prepared by the above methods in the fields of cold collision, cold chemistry,and precision measurements.