Diversity of animal behavior, as an essential part of biodiversity, is closely related to the ex situ conservation and behavior management of rare animals. We recorded the processes, contents, and surrounding habitat, derived from behaviors of semi-captive hamadryas baboons (Papio hamadryas) living in Guangzhou Chimelong Safari Park between December 2015 and August 2016. Both instantaneous scan sampling and focal animal sampling methods were used. The behavioral data were collected and coded based on the “posture-act-environment” (PAE) coding system which concerns posture, act, environment and the ecological function of behaviors. All observed behaviors of hamadryas baboons were classified and systematically encoded to construct the PAE behavior spectrum, and behavioral diversity was characterized simultaneously. A total of 18 postures, 120 acts and 208 behaviors were distinguished and the relative frequency of each behavior in relation to gender and age was described. Based on the ecological function of behaviors, these recorded behaviors were divided into 18 categories, including forage, eliminate, thermo-regulate, pair, mate, parent, affinitive, superior, threaten, aggression, submission, communicate, aggregate, rest, locomotive, play, beg, and miscellaneous behaviors. This ethogram extends previous behavioral lists and ethograms of non-human primate species constructed by our predecessors. Furthermore, two categories of behavior (play and beg) were enhanced in the non-human primates’ PAE behavior coding system. The characteristics of these two categories of behaviors were described and discussed, and hence, they are proposed to be new adaptive behavior to the captive environment. This research also probed the ecological function and adaptable significance for most behavior categories, separately. Finally, the index of behavioral diversity among different sex-age classes of semi-captive P. hamadryas were calculated on the basis of PAE coding system. Our results suggest that the behavioral diversity among different sex-age classes of semi-captive P. hamadryas were very close to one other at the overall behavioral level, and the more subdivided the behavioral segmentation was, the more obvious the displayed differences. It also proves that the utilization of the PAE coding system to classify, subdivide, and standardize the behavior of animals will improve the study of behavioral diversity.