The invention discloses a mobile phone photographing fixing device for an optical instrument, which comprises an eyepiece barrel clamping module and a mobile phone clamp, and is characterized in that the eyepiece barrel clamping module is provided with a base, the base is provided with an imaging hole, the base is internally provided with a spiral groove by taking the imaging hole as a center, the base is internally provided with an adjusting hand wheel, the adjusting hand wheel is internally provided with at least two clamping jaws, the clamping jaws are provided with limiting seam allowances which are clamped into the spiral groove for positioning, the adjusting hand wheel is provided with stop buckles, guide stop buckles and an adjusting hand wheel outer ring, the clamping jaws are provided with clamping jaw arcs and sliding grooves, the guide stop buckles are clamping into the sliding grooves, the base is provided with a circular disc, the inner side of the circular disc is provided with stop grooves, and the stop buckles are clamped in the stop grooves. The mobile phone photographing fixing device has the beneficial effects of practicability, low production cost, convenient use, realization of optical instrument imaging photographing by utilizing a mobile phone, convenience and rapid image acquisition, convenient operation, low cost, firm and stable barrel clamping and strong universality.