It is vital to improve the joint power density for the development of humanoid robots, especially for reducing the size of the anthropomorphic upper-limb joints. This paper presents a Wolfrom reducer scheme that utilizes the gear modification principle to achieve a more compact layout with fewer components. The Wolfrom reducer configuration is characterized by a wide range of reduction ratios, capable of achieving a maximum reduction ratio of approximately 1:500 within the same dimensions through different gear matching relationships. This allows a small rotor with relatively low torque to provide a large output torque. Additionally, this paper presents a specific design of a flat reducer demonstration prototype using this modified gear Wolfrom reducer scheme, combined with a small motor, to realize a dual-degree-of-freedom joint system suitable for humanoid robotic arms. Compared to traditional robotic joint systems, this system features a more compact structure that better fits the humanoid form, along with a hollow conduit for wiring, making it suitable for practical application environments such as the shoulder joints of humanoid robots.