The effective placement of proppant is crucial for forming artificial fractures with high conductivity. Current fracturing results indicate that the width of artificial fractures varies, and the migration and placement patterns of proppant in fractures with non-uniform widths are not well understood. This paper establishes a complex fracture model with non-uniform widths based on the Eulerian two-phase flow method, and validates it through physical experiments. The study analyzes the influence of pumping rate, proppant size, sand-to-fluid ratio, and fracturing fluid viscosity on proppant placement in complex fractures with non-uniform widths. The impact of these factors is evaluated using dimensionless effective propped fracture volume. The results show that: (1) Regarding the sand dune morphology, increasing the pumping rate reduces the equilibrium height and enlarges the sand-free zone near the fracture entrance; increasing the proppant size raises the equilibrium height, and larger sizes may cause sand bridging, leading to a sand-free zone at the fracture tip; increasing the sand-to-fluid ratio raises the equilibrium height and improves the uniformity of proppant placement; increasing the fracturing fluid viscosity reduces the equilibrium height and allows more uniform proppant placement at the fracture tip. (2) For the dimensionless effective propped fracture volume, the pumping rate and fracturing fluid viscosity show a linear negative correlation, while the sand-to-fluid ratio and proppant size show a linear positive correlation. Compared to other parameters, changes in proppant size have the greatest impact on the dimensionless propped fracture volume. (3) To optimize the conductivity of artificial fractures, it is recommended to use small-sized proppant, low sand-to-fluid ratio, high pumping rate, and high-viscosity fracturing fluid in the early stage to ensure better and more uniform proppant placement at the fracture tip. In the later stage, large-sized proppant, high sand-to-fluid ratio, low pumping rate, and low-viscosity fracturing fluid should be used to ensure full proppant filling in the near-wellbore region.