In order to measure the transmission wavefront of laser rods and to improve the edge diffraction effect of small-aperture laser rods measured by a general Tayman or Fizeau interferometer, a variable-inclination phase shifting Mach-Zehnder interferometer was proposed. In the proposed interferometer, the phase shifting reflector was placed on the electric linear rotating table. By adjusting the tilting attitude of the phase shifting reflector, the incident angle into the Mach-Zehnder interference cavity was changed. A laser rod with a certain length was placed in the test optical beam as the test object, and it could be used as a retarder in the equal optical path Mach-Zehnder interferometer to increase the optical path difference between the reference beam and the test beam, so the proposed interference system met the requirement of phase shifting. The optical path difference between the reference beam and the test beam changed each time the incident angle into the Mach-Zehnder interference cavity was transformed by the phase shifting reflector placed on the electric linear rotating table, thereby the phase shifting quantity was introduced to the coherent light. The phase shifting interferometry was realized under the interaction of phase shifting reflector and laser rob. The transmission wavefront of a laser rod (Nd:YAG) with the diameter of 6 mm and the length of 60 mm was measured by this interferometer, the peak-valley value (PV) and root mean square value (RMS) of the wavefront are 0.391λ and 0.056λ. The same laser rod is measured by ZYGO GPI XP interferometer, the peak-valley (PV) and root mean square (RMS) of the wavefront are 0.370λ and 0.064λ. The surface shape and numerical values of the two measurements are consistent, the comparison results show that the proposed interferometer can achieve high precision measurement of transmission wavefront of the laser robs. The proposed variable-inclination phase shifting Mach-Zehnder interferometer can realize periodic phase shifting only by using a reflector with adjustable inclination angle in the traditional Mach-Zehnder interferometer. It has high phase shifting precision and wide phase shifting range. The high precision phase modulation can be achieved by using conventional precision stepping motor. The proposed interferometer system is cheap and compact. The transmission wavefront of a small aperture laser rod can be measured by the variable-inclination phase-shifting system. The beam in the system can pass through the laser rod only once, therefore, the interferometer has obvious advantages in measuring the transmission wavefront of a small-aperture optical element with a certain length. It can effectively suppress the multi-beam interference and improve the edge diffraction effect of small-aperture optical elements.