The present invention belongs to the field of pharmaceutical chemistry, and relates to synthesis intermediates of a halichondrin B analog, and a preparation method thereof, wherein specifically the intermediates a compound represented by a formula I and a compound represented by a formula II are provided, and during the halichondrin B analog synthesis process, the production cost can be effectively reduced by using the intermediates, and the industrial production is easily achieved. The formulas I and II are defined in the instruction.