Abstract: The flexible support is the key component of fast steering mirror. The kinematic design of flexible support for fast steering mirror was introduced. According to the spatial relationship between constraints and degree of freedom, the mode of constraints and degree of freedom of flexible support was determined. The slender rod was used as the constraint element to construct four configurations of flexible support for fast steering mirror, and two new types of flexible support structures were obtained based on the classification of existing fast steering mirror mechanisms. The research results can provide guidance and basis for mechanism selection, optimization and engineering design.