Ultrafine SnO2/Sn nanoparticles encapsulated into an adjustable meso-/macroporous carbon matrix have been successfully fabricated by the in situ SiOx sacrificial strategy. The control over the void space in the carbon matrix effectively improves the accessibility of the SnO2/Sn toward an electrolyte solution. More importantly, the void space also provides an efficient means to accommodate the mechanical stress caused by the volume change of the SnO2/Sn over cycles. As a result, the enhanced electrolyte accessibility and suppressed mechanical stress improve the electrochemical performance regarding reversible capacity, cyclic stability, and rate capability. A reversible capacity of 1105 mAh g-1 is still retained after 290 cycles at 200 mAg-1, and the capacity still can keep at 107 mAh g-1 at a high current density of 10 A g-1.