An observational system for five-level wind speed, temperature,humidity and three-level wind direction is introduced in this paperThe data sampling and processing are conducted on an Apple-Ⅱ micro-computer and the sampling time is 10 seconds.The work consists of theprogram design and the measurement of humidity with the psychrom-eter.For ensuring accuracy the psychrometer coefficient A is remeas-ured and the errors in humidity measurements are analyzed in muchdetail.