A computer device and a host module thereof are provided. The host module includes a case, a motherboard, and a power supply unit. The case includes a first side plate, a second side plate, a front panel, a rear panel, and a separation structure. The rear panel is located on an opposite side of the front panel. The first side plate, the second side plate, the front panel, and the rear panel enclose an internal space. The separation structure is located in the internal space, extends from the first side plate to the second side plate, and divides the internal space into a first part and a second part. The second part is located under the first part. The motherboard is disposed in the first part. The power supply unit is disposed in the second part, and is electrically connected to the motherboard.