The invention discloses a fiber strand rough length measuring instrument winding preventing device, and relates to the field of detection in the cotton textile industry. According to the invention, a length measuring roller is arranged between a left wallboard and a right wallboard, the top end of the left wallboard and the top end of the right wallboard are provided with a pressure roller support shaft, a pressure roller is connected with the pressure roller support shaft through a left pressure roller hanger and a right pressure roller hanger, and the pressure roller is in friction transmission with the length measuring roller. The winding preventing device is characterized in that the pressure roller support shaft is further provided with a yarn baffle plate hanger, a yarn baffle plate is connected with the pressure roller support shaft through the yarn baffle plate hanger, the yarn baffle plate is contacted with the pressure roller, the yarn baffle plate is an arc-shaped baffle plate, the radian of the yarn baffle plate is consistent with that of an outer arc of the pressure roller, the arc length of the yarn baffle plate is 430mm, the width is 20mm, the side, which is contacted with the pressure roller, of the yarn baffle plate is connected to a wool felt pad, the yarn baffle plate hanger comprises a left yarn baffle plate hanger and a right yarn baffle plate hanger, and one side of the pressure roller support shaft is provided with a handle. When a fiber strand is sticked and winds upwards, the yarn baffle plate and the wool felt pad keep off the up-winding fiber strand, the fiber strand falls back to the part below the length measuring roller again, the test goes on continuously, and occurrence of a sticking and winding phenomenon is avoided. The winding preventing device disclosed by the invention is simple in structure and convenient to use, improves the work efficiency and reduces repetition work.