This article presents a systematic approach for attitude determination of unmanned aerial vehicles (UAV) based on common-clock GPS/BDS receivers. With properly configured receivers on UAV, the baseline vectors and the platform orientation defined by these vectors can be measured. In addition, on-the-fly (OTF) carrier phase ambiguity resolution method is applied through single-difference (SD) model with common-clock technology. The feasibility of the whole scheme as well as accuracy and reliability are demonstrated by kinematic experiment.