Hydraulic fracturing is a key technology for the development of unconventional oil and gas reservoirs, where the transport and placement of proppants within fractures determine the production. To clarify the transport of proppants during the propagation of three-dimensional complex fractures and to optimize the stimulation parameters, based on the previously established model for the propagation of three-dimensional complex fractures and the transport of proppants, this paper conducts a coupled study on the complex fracture propagation and proppant transport considering the fracture height growth. The model considers the stress interference between fractures, fluid flow and proppant transport within the propagating fractures, and the interaction between hydraulic fractures and natural fractures in three-dimensional space. Based on the actual geological and well-logging data of a vertical well in the coal seam of the Haishiwan mining area, Gansu Province, with the propped area and conductivity within the fracture as the objective functions, the fracturing parameters are optimized, including proppant size, total amount of proppant, fluid viscosity, and injection rate. The results show that: (1) Due to the low in-situ stress of the coal seam, most fractures propagate within the coal seam, but near the wellbore, due to high net pressure, the fractures show significant cross-layer propagation; (2) Larger-size proppants settle quickly, forming a proppant dune at the bottom of the fracture. To ensure both propped area and fracture conductivity, it is recommended to use 30/50 mesh proppants; (3) When the total amount of proppant increases from 50 m3 to 100 m3, the propped area increases by 33%. Further increasing to 140 m3 results in a negligible increase on the propped area, thus 100 m3 is recommended; (4) Under high injection rates, the carrying capacity of the slurry is stronger, significantly increasing the propped area, and an injection rate of 12 m3/min is recommended. This study can provide an optimized design model and theoretical guidance for field-scale design.