Abstract: The Monte Carlo particle transport code program MCNP is used to establish a cobalt-60 irradiation device model and simulate the peripheral spatial dose field distribution outside the irradiation station in the irradiation room. The Cartesian coordinate system is established with the center point of the single-rack source frame as the coordinate origin. Considering the γ-rays non-self-absorption and the γ-rays self-absorption of cobalt-60 source, the dose rate distribution of the air surface at intervals of 10 cm along the coordinate axis and the variation law of dose rate on the coordinate axis are studied. The results show that the dose rate of the peripheral spatial dose field is relatively small, when the irradiation products of the irradiation room occupy all the irradiation stations. The variation law of dose rate on the coordinate axis of the single-rack source frame is more consistent with binomial fitting function. In the case of γ-rays self-absorption of cobalt-60 source, the dose rate near the coordinate axis of the single-rack source frame is obviously low, and the high-dose-rate region of the air surface moves to both sides as air surface moves away from the single-rack source frame. In the case of γ-rays non-self-absorption of cobalt-60 source, the high-dose-rate region of the air surface at the end face of the single-rack source frame is always located near the coordinate axis. The theoretical simulation calculation and analysis of MCNP has important practical guiding significance for the peripheral spatial dose field outside the irradiation station in the irradiation room of the cobalt-60 irradiation facility.