The formation volume factor of crude oil is the key parameter for oil and gas reservoir reserves calculation. Due to the susceptibility of the PVT(Pressure-Volume-Temperature) experimental method to sample representativeness and its high cost, empirical equations are commonly used in the field to predict volume factors. Fuman Oilfield, with its Ordovician carbonate reservoirs, is characterized by wltra-deep, high temperature, ultra-high pressure, and diversified fluid types across different blocks, leading to a poor performance when using existing empirical equation to predict oil volume factor. In response to this issue, after analyzing and evaluating the applicable conditions of the existing volume factor empirical equations, we have developed empirical formulas to calculate the saturation pressure and volume factor of black oil and volatile oil under formation conditions in Fuman Oilfield Ordovician carbonate reservoirs. By comparing with PVT experimental saturation pressure and formation oil volume factor, the average prediction errors were all less than 5%, which satisfied the demands of oilfield exploitation and production management. The research results offer valuable insights for determining the volume factors of crude oil in high-temperature, ultra-high-pressure formations of the same nature within the Tarim Basin.