An off axis reflective collimator is designed for multi-parameter detection of white light sights. In order to address the problem of large error of the primary mirror face form due to low frequency vibration of the collimator under operating condition, a flexible support scheme for the back of the primary mirror is proposed, and the important structural parameters of the flexible support for the primary mirror are optimized. At the same time, the properties of the RTV adhesive is analyzed and the effective property and equivalent module multiplier of the annular RTV adhesive are calculated. The simulation results show that the RMS and PV values of the surface error of the primary mirror assembly are 0.79nm and 3.66nm, respectively, under the action of 1-g gravity, which can meet the system requirements for wavefront aberration of the collimator. The first mode frequency of the whole collimator is 496.38Hz, which has a good ability to resist low frequency vibration. Under the action of thermal coupling, the face form errors of the primary mirror face form variations all meet the design requirements of RMS valueand ≤λ/30 PV value ≤λ/10.Under the harmonic response analysis, The maximum stress under 1000N force is less than the yield limit of the material. The dynamic performance and surface accuracy of the off-axis reflector collimator with flexible support can meet the design requirements.