Highly-catalytic, cost-effective, well process-compatible, and highly-stable hydrogen-evolving catalysts are increasingly becoming key catalysts in realizing monolithic electrochemical solar water-splitting devices. However, the typical noble metallic catalysts seriously restrict the industrialization of electrochemical solar water-splitting devices on account of their poor storages and high costs. Low-cost, high-catalytic and non-metallic catalysts pave the promising way for the industrialization process. Molybdenum sulfide has emerged as a type of potential catalyst with high-activity and stability for the hydrogen-evolving reaction (HER) in the acidic condition, nowadays gradually becoming a research hotspot in solar-water-splitting. The process preparation of high-efficient molybdenum sulfide catalyst is consequently extremely important for enhancing the solar-to-hydrogen efficiency. In this paper, we synthesize highly-catalytic, low-cost, and highly-compatible non-metallic amorphous molybdenum trisulfide catalyst based on a simple wet chemical approach at room temperature for hydrogen-evolving reaction, followed by extensive studies of the effects of the mass loading of catalyst on the catalytic capacity and the solar-to-hydrogen performance of solar-water-splitting devices in series. When the mass loading is 0.5 mgcm-2, the MoS3 catalyst exhibits the promising HER activity. the surface of catalyst appears to be rough, porous, nano-sized architecture and the thickness is around 2.0 m, which simultaneously enlarges the electrochemically active area and reduces charge transfer impedance, accelerating the electron transport to electrochemically active site and improving the interfacial charge transfer. Besides, the HER catalytic activity is illustrated in a wired solar-water-splitting device. The current density can achieve the maximum values of 7.51 and 3.28 mA/cm2 corresponding to 0 and 0.8 V vs. RHE, and the onset potential is 1.83 V, comparable to the open circuit voltage (1.90 V) of two amorphous silcon cells in series. Therefore, we conclude that for amorphous molybdenum trisulfide catalyst there exists an optimized mass loading, with which an optimized catalytic capacity (260 mV vs. RHE at 10 mA/cm2 and tafel slope of 68 mV/dec) can be achieved. Further, by using the catalyst as a cathode for the solar-water-splitting devices in series, the catalyst can efficiently reduce the overpotential and improve the current output for the device, thereby potentially achieving a higher solar-to-hydrogen efficiency.