Abstract: ‍ ‍With the rapid development and progressive application of passive radar technology， interference problems are a growing concern. This paper took linear Frequency Modulation（LFM） interference， which greatly affected the performance of OFDM-based passive radar， as the research object， and theoretically analyzed the interference pattern and characteristics of Multi-cycle LFM interference to OFDM-based passive radar according to the LFM interference signal model， and deduced the relationship between the interference bandwidth and the associated time delay width， and then proposed an adaptive Multi-cycle LFM interference suppression method. The proposed interference suppression method first detected the interference in the frequency domain and estimated the LFM interference bandwidth， then constructed an interference subspace on the Range Doppler spectrum by selecting a slow time dimensional sequence according to the interference bandwidth， and finally achieved the suppression of Multi-cycle LFM interference by orthogonal projection of the interference subspace. The effectiveness and robustness of the proposed method for interference suppression are verified by simulation under different conditions of interference intensity， interference bandwidth and LFM period， using the base-improvement factor as the evaluation index.