Abstract: An observation system was developed to measure microclimate (temperature,humidity and wind speed) within canopies of crops.Four groups of sensors are used,which are calibrated in laboratory,and compared and tested under natural conditions.The observation of microclimate was conducted in a maize field at Yucheng Experimental Station in Aug.1999.The observation results showed good correspondence with basic principles of microclimate.This instrument gives a more precise and real-time measurements than previous ones.