Diffuse laser cooling (DLC) provides a compact, robust, and scalable approach to generating cold-atom ensembles, offering significant potential for ground-based and spaceborne microwave atomic clocks. However, the performance of DLC systems remains limited by the weak atom-light interaction arising from their relatively low atomic density. This limitation is characterized by the optical density (OD), which quantifies the effective interaction strength between the atomic ensemble and the probe light and strongly influences the achievable signal-to-noise ratio (SNR). Although quasi-one-dimensional (quasi-1D) DLC extends the probe interaction length and improves atomic utilization, increasing the local atomic density within the interrogation region remains challenging. Here, we demonstrate a magnetically enhanced quasi-1D DLC system that simultaneously maintains the extended interaction length and increases the atomic density through a two-dimensional magnetic-field gradient. By spatially compressing and accumulating atoms near the probe axis, we enhance the OD of a 70-cm-long cold rubidium ensemble from 2.49 to 3.94, representing a 58% enhancement and an equivalent increase in the local atomic density. The dependence of the OD on the magnetic-field gradient, probe intensity, beam size, and cooling-light polarization is systematically investigated. This work establishes a practical pathway for enhancing optical interrogation efficiency and could pave the way for the development of high-performance DLC-based cold-atom clocks and quantum sensing systems.