Grating constant measurement experiment especially reflect the characteristics of optical experiment， which requires high coarse adjustment and strong adjustment sequence．It can cultivate students to develop thehabit of careful observation and thinking，and improve students’hands-on ability in experiments． In theexperiment，there are some problems，such as the blurred reflection image due to the unfocused telescope，the too long time of coarse adjustment of the telescope and the unclear grating adjustment requirements，which lead to the delay of the experiment．In-depth analysis of the above problems has been done，and some solutions are  found．The focus of the telescope is adjusted by a plane mirror sticking close to the light outlet of the telescope， and the coarse adjustment of the telescope is assisted by the parallel light tube．The grating adjustment requirements are summarized as: “Three scales and two coincide，equal height of the spectral lines; Both are satisfied，and then measure the diffraction angles”．