The invention discloses a float type oil storage tank. The float type oil storage tank comprises an oil tank body, wherein an oil cavity is formed in the oil tank body; the bottom of the oil cavity has two oblique plane structures which are recessed; the lowest position of the bottom of the oil cavity communicates with an oil tank drainage pipe; a float guide column is further vertically arrangedin the oil cavity of the oil tank body fixedly; the oil cavity further comprises a float; the density of the float is smaller than that of oil; the float has a disc structure; a guide hole is formed in the axis of the float in a hollowed-out manner; the float guide column penetrates in the guide hole of the float; and the float can move in the up-down direction along the guide column along with change of the depth of liquid in the oil cavity. The float type oil storage tank is simple in structure; and a float type oil absorbing structure is adopted, and thus, the circumstance that an oil absorbing tube directly absorbs precipitates at the bottom is avoided.