Spatial parameter is spatial information used for expressing the effect that human ears perceive a sound field. The bit allocation of the spatial parameter is one of core technologies of spatial audio coding. The invention discloses a bit allocation method with the spatial parameter fined step by step and the method includes the steps of: first carrying out frame-dividing processing to an input signal; allocating frequency band of each frame signal according to bark band rule after time-frequency transform and selecting bit allocation mode; and then carrying out bit allocation to all parameters of inter-frame, intra-frame and intra-frequency band according to the selected allocation mode, realizing the bit allocation with the spatial parameter fined step by step and designing an application device based on this. The method gives more bit allocation to a human ear part which perceives the most amount of information most sensitively and less bit allocation to a human ear part which perceives insensitively, thus achieving the purpose of effectively improving coding efficiency on condition of ensuring transparent timbre.