Understanding the suitability of wildlife habitats and their activity rhythms is of great significance for the scientific protection of forest ecosystems. The roe deer (Capreolus pygargus), an important component of the forest ecosystem, plays an indicative role in vegetation renewal and the distribution of sympatric species. Understanding its habitat suitability and activity rhythms is the foundation for restoring biodiversity. This study, conducted from June 2022 to May 2023 in the Beijicun Nature Reserve, utilized a combination of transect surveys and camera trapping methods to collect information on roe deer activity. A total of 35 transects and 140 infrared cameras were randomly deployed in the reserve. The MaxEnt habitat modeling and kernel density estimation methods were used to analyze the habitat suitability and activity rhythms of the roe deer. The results showed that: (1) The average AUC value of ROC curve evaluation results of MaxEnt was 0.839, which could really reflect the actual distribution of habitat suitability of roe deer in the study area; (2) Among the 14 variables used in the study, the lower the probability of occurrence when the distance from the river is the key variable affecting the habitat selection of roe deer, with a contribution rate of 34%. Secondly, coniferous and broadleaved mixed forest, evergreen coniferous forest, forest path, altitude, grass and residents area were the secondary variables affecting the habitat quality of roe deer; (3) The suitable habitat and middling-suitable habitat of roe deer in the reserve are 240.44 km² and 490.64 km², accounting for 17.48% and 35.67% of the total area of the study area, and are mainly distributed in the central and eastern parts of the reserve, while the suitable habitat area in the west is less and the fragmentation is more serious; (4) Activity rhythm analysis indicated that the roe deer reached their daily activity peak at around 9:00 am. Different seasons showed variations in the activity rhythms of the roe deer, with crepuscular activity patterns observed in the warm season and delayed/advanced peaks in the morning and afternoon during the cold season. Based on the research results, the following conservation suggestions are put forward: (1) Strengthen the control of human activities around the reserve, and protect roe deer population according to different human disturbance intensity; (2) The fragmented habitats were connected as a whole by strengthening habitat connectivity management and constructing habitat corridors, and the communication among roe deer individuals in the protected areas was promoted. The results provide fundamental data for the protection and restoration of the northernmost roe deer population in China and are of significant importance for promoting biodiversity conservation in the region.