Up to June 2005,L band digital radiosondes are used in 36 upper-air observation stations in China.In order to understand the observation error characters,the error analysis is made about the observed temperature data of L band digital radiosonde from March to May of 2005.The mean and root mean square biases of observation minus background field of T213 model,which is called OMB,are calculated.Bessel fitting technique is used to separating out observation error from OMB.The results show that comparing with Model-59 radiosonde observation data,there is no obvious difference(usually in 0.2℃)in the mean of OMB.But a great reduction is made in random errors of temperature of L band digital radiosonde:at 12Z and at 00Z 500～300hPa about 0.2℃;at 00Z above 300hPa,about 0.4℃,accounting for the 25% of the random errors of temperature for Model-59 radiosonde.