Astronomical three-dimensional spectral imaging technology is a real-time spectral acquisition technology for all source targets in the observation field of view. It can simultaneously obtain the spectral domain and two-dimensional spatial domain information of the target by single sampling. Optical fiber integral field unit (IFU) is the key component of astronomical three-dimensional spectral imaging technology. The image plane information is subdivided into several units and transmitted to the spectrometer through the segmentation of the received image plane. In this process, the two-dimensional spread source target is reorganized into a non-interference linear array for sampling and extraction by the spectrometer, which can effectively improve the temporal resolution of astronomical observation. This paper introduces an IFU with 242 fiber units, currently applied to the fiber array solar optical telescope (FASOT-1B) system of Yunnan Observatory of the Chinese Academy of Sciences. In order to meet the index requirements of FASOT-1B and obtain the observation effect of high transmission efficiency, high spectral resolution and high time resolution, the IFU adopts the structure of a microlens array and fiber array. The microlens is a regular hexagon spherical mirror, and the spatial filling rate is nearly 100%. Considering the design parameters of the front telescope system and the back-end spectrometer system of the fiber integral field-of-view unit, a pair of 11×11 microlens arrays is an optimized design. The distance between adjacent microlens is 300 μm, and each microlens corresponds to the sky area of 1.5″. The received light is incorporated into the corresponding fiber core with the focal ratio F/8.2. The relationship between fiber core diameter and spectral resolution of the spectrometer is analyzed systematically. The design specifications of the fiber are 35/105/125 μm. This parameter can not only meet the requirements of the optical fiber to receive all the optical information transmitted by the microlens but also can obtain the spectral resolution and relatively short slit width to meet the system’s requirements. The influence of fiber diameter and micro-hole depth on the actual incidence focal ratio of the IFU array is quantitatively analyzed, and the micro-hole size is selected as 130 μm in diameter and 3 mm in depth. A two-dimensional arrayed optical fiber is reorganized at the pseudoslit end, and the optical information is imported into the spectrometer in a linear arrangement. The distance between adjacent fibers is 130 μm. The problem of IFU fiber fixation and polishing is solved. The average energy transmission efficiency of IFU is 77.7%, and the RMS is 1.6%. All fiber output focal ratio EE90 is slower than F/7. The RMS value of the lateral (alignment) offset of the IFU pseudo-slit end fiber is less than 2.7 μm, and the RMS value of the longitudinal (perpendicular to alignment) offset is less than 1.8 μm. After the installation and debugging of IFU and FASOT-1B systems, the confirmatory observation was carried out, and the Stokes spectrum of the MgI chromosphere in the solar NOAA12738 active region was successfully obtained. This IFU has also become the first fiber plus convex lens IFU independently developed and applied to scientific observation in China.