Abstract: Working stiffness is an important reference index for the performance of ultra-precision spindles. In order to solve the problems that the applied load is difficult to control accurately and the displacement measurement method is not accurate, which are common in non-contact loading measuring devices for ultra-precision spindle working stiffness testing, a new working stiffness measurement method based on the displacement method was studied. Firstly, the paper introduces the principle of the method for measuring the working stiffness of the spindle, and then proposes a spindle working stiffness measuring device based on the principle. Secondly, the device adopts non-contact loading and measurement, which can realize the accurate and stable control of the loading load under the rotating state of the spindle, and realizes the accurate measurement of the spindle displacement through multiple high-precision displacement sensors. Finally, the experimental verification of the device's testing performance showed that the device's repeated error was less than 5%, and the test results had high reliability, which could meet the requirements for testing the stiffness of ultra-precision spindles.