Silicon suboxides (SiOx, 0 < x < 2) have been shown commercial prospect in lithium-ion batteries because of relative high capacity and mild volume expansion. However, few methods are available to prepare oxygen-tunable SiOx. Herein, we introduce a bottom up strategy to realize the consecutively regulation of oxygen content in SiOx via stepwise oxidizing silicane/siloxene precursor. Experimental results show that x value rapidly increases up to 1.5 and then rises extremely to 2.0 with minor slope. Furthermore, theory calculations indicate oxygen is preferentially inserted into Si–Si bonds to form buckled Si–O–Si limited to SiO1.5H with higher driving force than the following Si–OH formation which is well consistent with the experimental results. Virtually, nominal SiOx is substantially the mixture of Si, SiO0.5, SiO, SiO1.5 and SiO2 with SiO1.5 as the predominate component. Among the representative SiOx samples, SiO1.47 exhibits the optimal electrochemical performance with reversible capacity of around 700 mAh g−1 and almost 100% capacity retention at 0.5C (1C = 1500 mA g−1) after 300 cycles because of higher Li-ions diffusivity and less fracture. In addition, 95.4% capacity retention is achieved after 100 cycles at 0.2C in full-cell system.