In this paper, the design of in-plane modal sensor for annular plate structure is carried out. Based on the in-plane dynamics of annular plate under complex boundary conditions, the strain distribution of annular plate of each in-plane modal order is obtained. The piezoelectric film, which is completely covered over the plate, is discreted, and the polarized distribution of PVDF film is modeled and solved by linear optimization method, in which the polarization directions of PVDF are employed as the design variable. The charge response under in-plane modal of annular plate is the target function and constraint condition. Efficiency and correctness of the designed modal sensor for the target order frequency extraction and non-target frequency filtering are verified through frequency response prediction. Based on this, the influence of complex factors such as boundary constraint on the in-plane modal sensor is revealed by numerical examples.