Financial flexibility makes the enterprise deal with adversity and grasp the advantage of investment opportunities through the reasonable arrangement of the distribution of cash flow quantity and the distribution of time,so as to improve the adaptability and operating performance of enterprises.Therefore, the paper studies the effect of operating cash flow fluctuation on R&D investment from the perspective of financial flexibility. The empirical results show that the fluctuation of operating cash flow negatively affects R&D investment. Then financial flexibility has a positive adjustment to the correlation of them. By increasing the financial flexibility to weaken the impact of operating cash flow fluctuations on R&D investment.