The tube scanner is a key part of the photon scanning tunneling microscope (PSTM). The sensitivity, resolution, scanning range and the linearity of PSTM are quite relevant to the study of the tube scanner. In this article, a new experimental method to measure the deflection sensitivity of the PZT tube is reported. The tube travel range, its linearity, and the coupling betweenxoryandzdirection are analyzed. The theoretical formula for the coupling effects are also derived. With careful design the tube scanner coupling can be neglected and the experimental results show that the linearity of the large travel tube is satisfactory. Some images of PSTM demonstrate convincingly the system performance. The imaging of Langmuir–Blodgett (LB) films and fish scale plates is a significant application of PSTM in the fields of organic materials and living specimens. ©1997 American Institute of Physics.