Abstract: There are two kinds of operation mode of plant protect multi-rotor UAV, hover and fixed-speed flight, so corresponding working modes of spectral remote are needed. However, general-purpose remote sensing equipment couldn't satisfy the needs. A set of liquid crystal spectral imaging device was designed to meet the requirements of low-altitude spectral remote of multi-rotor UAV based on the principle of two-dimensional optical splitting. Firstly, the hardware and the software of the device were developed to realize the synchronization of three modules: the acquisition module, the control module and the communication module. The acquisition module consists of a16-bit CCD grayscale camera, a color aberration lens, a liquid crystal tunable filters (LCTFs), and a UV filter. The control module consists of a microcomputer controller and a USB connector. The communication module consists of a data transmission device, BEIDOU positioning systems, and the ground workstations. The software was developed to control hardware for working synchronously and analyze data. The functions of software were not only for parameter adjustment before formal capturing, but also for spectral images analysis alone and achieving spectral abstraction. Secondly, the data acquisition method based on the principle of device was studied. The relationship between the flight speed, altitude and capturing parameters of the device was established, which guaranteed the quality of spectral images, the possibility of image mosaics, spectral continuity and stability of the captured spectral images. Thirdly, indoor and outdoor experiments were carried out to test the device performance and data acquisition method. The indoor experiment was performed in the wind tunnel laboratory of South China Agricultural University by a stepper motor equipped. Compared with the millimeter-defocus blur spectral images, and the micro motion blur spectral images, the original images taken indoors were 10 and 15 times clearer respectively. Furthermore, image mosaics could be achieved based on feature point algorithm. The outdoor experiment was carried out in Xinxiang, Henan Province, China, with a Quadrotor UAV equipped. The results showed that the original images taken outdoors had high-quality, and the spatial resolution was up to 1 392×1 040 pixels. The spectra abstracted from original images were stable and reliable. The spectral range was 400-720 nm, and the spectral step was up to 2 nm. Both the comprehensive indoor simulation tests and the outdoor tests showed that the liquid crystal spectral imaging device developed in the paper could obtain qualified spectral images, and showed that the device could match two operating modes of multi-rotor UAV, hover and fixed speed motion. Based on the design of direct coupling optical path, the whole set of device is compact structure, vibrate resistance, high reliability and stability, and suitable for plant protection working. The new method and the device were provided for low-altitude remote sensing of multi-rotor UAV in the paper, which is expected to be applied to precision spraying, crop prescription map generation and other related fields.