In order to facilitate the low-cost, ultra-light weight and easier operation, the authors constructed a smartphone based unmanned aerial vehicle (UAV) low altitude oblique photogrammetric system by integrating DJI Phantom 4 UAV flight platform with good flight traits and Nokia 808 PureView mobile phones with good image-taking functions. In this system, relative functions of multi-camera imaging system with mobile phones were optimized, and the module design method was adopted for the system which includes the measurement of improving image quality, and the design of flight control module used for automatically image-taking control developed by open source flight control system, the design of the POS module and some other means. The integrating mode by the multi-camera system adopted as payload and flight platform was discussed, and then the working flow of the integrated system was concluded. The system was used for different applicable fields, i.e., real estate surveying, open-pit mine monitoring, and 3D reconstruction of urban buildings. The application results assessed by check points measured with field work and manual vision inspect indicate that the real-world 3D model has better texture quality, and the digital survey and mapping products, real-world 3D model and digital linear graph as well as some other means have higher geometric accuracy with centimeter level. The proposed system will be very important for boosting the development of UAV low altitude oblique photogrammetry in terms of practical demands.