The initial designed structure of the diameter measuring gauge of filter rod forming machine is too large, so that it cannot be installed in the limited space of filter rod forming machine. Because of this, the structure of the diameter measuring gauge is redesigned in order to overcome the space constraints of filter rod forming machine. Firstly, the diameter measuring gauge of KDF2、KDF3 type filter rod forming machine is redesigned by combining the advantages of the theory of inventive problem solving (TRIZ) and constraints (TOC). Next, through constraints theory, finding the main contradictions of initial design and then contradictions can be eliminated by using inventive problem solving theory. Finally, diameter measuring gauge of filter rod forming machine design should be available, and the product design successfully. It is the first time that this type diameter measuring gauge is designed and installed on the KDF2、KDF3 type filter rod forming machine successfully across the country.