Time resolution in the picosecond to nanosecond range is difficult to achieve for a hard X-ray free-electron laser device. To solve this problem, a split-delay optical system design for a hard X-ray free-electron laser device currently under construction in Shanghai is proposed. The design is based on crystal diffraction, the delay time range is calculated, the system throughput is simulated, and a prototype is built and verified. The design can split a single X-ray pulse into two fractions using the spatial division method, and a time delay is introduced between the fractions by using different path lengths. The prototype can operate over a wide and continuous energy range between 7 and 11 keV and provide a delay from -15.4 to 503.3 ps. Throughputs of 33.54% (upper) and 33.64% (lower) for the split-delay optical system were simulated by Shadow, meeting the objective of a 1∶1 ratio. An alignment experiment for the prototype was conducted with a green laser, and the results demonstrate that the prototype can recombine the two beams after spatial division, laying the groundwork for future X-ray verification experiments. The design has the advantages of a small size, wide delay range, and continuously adjustable incident energy and delay time, which can facilitate the development of a split-delay optical system for the Shanghai hard X-ray free-electron laser device.