Stimulated-emission-depletion (STED) nanoscope achieves super-resolution imaging by using a donut-shaped depletion beam to darken the fluorophores around the excitation spot. As an important factor determining the resolution of imaging, the coaxiality between the excitation and the depletion beam is required to be maintained at the nanoscale, which is often degraded by various interference such as ambient vibration and temperatures etc. Here, we propose a specially designed STED illumination module to guarantee the coaxiality between the two beams while modulating the phase of the depletion beam. This STED illumination module can realize phase modulation, polarization adjustment, pulse delay and two beams coaxial at the same time. With the experiments, the module can guarantee the two beams are stably coaxial for a long time. We imaged fluorescence particles with diameter 40 nm and got images of 40 nm full width at half maximum. Adjacent microfilaments at 80 nm being clearly distinguished with our STED nonoscope demonstrates that it could be well applied to biological samples.