The C-field current stability of rubidium atomic fountain clock can affect the second-order Zeeman frequency shift of the clock. Traditional methods to optimize the physical system of the C-field are complicated and difficult to meet the miniaturization requirements. Starting from the circuit system of rubidium atomic fountain clock, this paper puts forward the method of optimizing C-field circuit by using chip current source. Firstly, the influence of the chip current source output fluctuation on the second order Zeeman frequency shift of the rubidium atomic fountain clock is analyzed and the relationship between the second order Zeeman frequency shift of the rubidium atomic fountain clock and the output current of the C-field chip current source is obtained； secondly, the measurement experiment of VC12MA current source is carried out. The experiment shows that when the C field is generated by VC12MA current source, the Allan variance of the output current value is 2.24×10-9, and the relative disturbance to the second-order Zeeman frequency shift of the rubidium atomic fountain clock is 1.78×10-17. The frequency stability of the second-order Zeeman shift of the rubidium atomic fountain clock is improved from the original 10-16 order to the optimized 10-17 order. The method presented in this paper has great application value in the performance improvement and miniaturization of the rubidium atomic fountain clock.