Abstract: Based on the observation and analysis,the researcher raised doubts about the calculation model of the warp beam instantaneous linear speed controlled by the electronic let-off system equipped with no feed back roller device.According to the document concerning the study of calculation model of electronic let-off at present and the latst information of Karl Mayer,the warp ends are regarded as some stiff material when calculating the warp beam let-off instantaneous speed which is used as basis for sending the signal to control the instantaneous warp beam let-off.It is pointed out that the tolerance resulting from this calculation belongs to a micro tolerance inherent from this let-off system and can not be corrected by optimizing its operation.And a qualitative analysis of this tolerance is done in this article.However,its quantitiative analysis is very complicated and further research as an individual subject is suggested.