This paper proposes focal surface occlusion to provide focal cues of occlusion masks for multiple virtual objects at continuous depths in an occlusion-capable optical see-through head-mounted display. A phase-only spatial light modulator (PSLM) that acts as a dynamic free-form lens is used to conform the focal surface of an occlusion mask to the geometry of the virtual scene. To reproduce multiple and continuous focal blurs while reducing the distortion of the see-through view, an optical design based on afocal optics and edge-based optimization to exploit a property of the occlusion mask is established. The prototype with the PSLM and transmissive liquid crystal display can reproduce the focus blur of occluded objects at multiple and continuous depths with a field of view of 14.6°.