A new method for cold atom number stabilization in a integrating sphere cold atom clock is proposed. The stabilization of cold atom number is realized by periodically monitoring the absorption signal of cold atom, adjusting the diffraction efficiency of acoustic optical modulation in cooling laser, and changing the cooling light power. The loop function of the cold atom number stabilization system is deduced, and its suppression effect on the fluctuation of cold atom number is analyzed. The normalized fluctuation of stabilized cold atom number is 1±0.001 in 3 h, and the maximum suppression of power spectral density is about 30 dB in the range of 0.001-0.2 Hz. The reason for fluctuation suppression is that the stabilization loop not only compensates the output light power of cooling laser, but also corrects the cold atom number drift induced by environment. When the cold atom number is stable, the atom clock frequency stability induced by the fluctuation of cold atom number is decreased to 7×10 -14τ-1/2 ( τ is the integral time).