This paper analyzes the positive and negative impact of grandchildren caring time on older people's health. The literature suggests that with the increase of grandchildren caring time, the accelerated increase rate of the positive impact on the middle and old-aged people gradually decreases, while the accelerated increase rate of the negative impact gradually rises. Therefore, the total effect demonstrates a trend of first rising and then declining. This paper empirically tests this hypothesis using the cross-section data of China Health and Retirement Longitudinal Study in 2015. The regression results based on both the overall sample and the sub-sample show that with the caring time increasing, the probability of self-reporting health deterioration of the middle and old-aged people declines first and then rises. This paper, comparing the actual grandchildren caring time, the optimal caring time, and the time that the influence of caring for grandchildren equaling to no caring for grandchildren, finds that the Chinese middle and oldaged people spend too much time caring for their grandchildren.