Warp spacing and pickspacing are important parameters that have significant effect on the visual, physical and mechanical properties of fabrics. Thus, to have a fabric with desirable properties, these two parameters play the key role. Spacing has affected by different factors so that identity of these factors is helpful to control the regularity of spacing. Position of the cloth fell is one of the effective elements on the pickspacing. This effect becomes more remarkable in the fabrics with more picks per inch. When weaving is started, the cloth fell gradually finds its correct position by moving away from the weaver. This position is maintained as long as the loom runs satisfactory. If there is a variation in the cloth fell position, there will be some changes in the pickspacing. These changes can reduce the quality of woven fabric. In this work, an electronic system was designed to measure the cloth fell distance dynamically during weaving process. This system consists of electronic sensors to sense cloth fell distance from front position of the reed. To install this system on the loom some various methods were studied and the best status was selected. This system has high accuracy and high speed in processing compared with other measuring methods. In this system, the duration between contact of the reed with the cloth fell and reed reaching to front Position of the Reed is measured by using the sensors and the equation of the reed motion is used to convert the measured duration into distance. In this study, the equation of the reed motion was calculated by theoretical and experimental method. Finally, the theoretical method was selected for calculating the cloth fell distance because this method is more accurate. Furthermore, in this work, circumstance of effects of the warp tension on the cloth fell distance and pickspacing was studied. To make a study of this subject, some fabrics under different warp tension were woven and for each sample, cloth fell distance by using the mentioned system, and pickspacing by using the image analysis were calculated. After that, the simulation of behavior of warp and fabric in the zwick and also, the statistical methods have been used to analyse the obtained results. statistical analysis of the results shows that there is a significant difference between average of the various sets of woven fabric that confirms the effect of warp tension on the cloth fell distance.