Policy instruments are considered to be specific means or measures taken by the government to solve public problems, and one policy can be regarded as the combination of objectives and various policy instruments. In the process of ecological governance, the degrees of policy instruments' stimulation to the behavior of local farmers are different, which further leads to different policy effects. The understanding of the influence of different policy instruments can provide a scientific reference for instrument selection and policy optimization. Taking Yanchi County as an example, using the data set of policy instruments constructed from 316 ecological policies issued by Yanchi County from 1983 to 2017 and based on the impulse response and variance decomposition method of VAR model, this paper quantitatively studies the impacts of various policy instruments that include mandatory instrument, hybrid instrument, voluntary instrument and ten sub-instruments on farmers' behaviors of farming, grazing, and afforestation. The results show that:(1) the impact of policy instruments on farmers' behaviors is time-sensitive, which would reach the maximum within 2 to 3 years after the instrument was implemented, and then gradually dwindle and disappear within 7 to 10 years. (2) Generally speaking, the impact of policy instruments on farmers' behaviors is relatively small, with an impulse response ranging from 0 to 0.30, indicating that the farmers' behaviors are also affected by many other factors. (3) The 10 years cumulative impact is in descending order of the mandatory instrument, hybrid instrument and voluntary instrument; The two instruments, direct provision and regulation, have the greatest effects. Farmers' behavior of grazing is most stimulated by policy instruments, followed by farming and afforestation. (4) The instrument of direct provision has the greatest positive impact on farming behavior, with a maximum impact of 0.30; the instrument of regulatory may inhibit the growth of livestock numbers in the short term, while the instruments of direct provision and subsidy may promote the growth of livestock numbers. There are fluctuations between positive and negative in the impulse response curves, indicating that there has been a long-term game between the government and farmers in livestock breeding. Only the instrument of regulatory has a positive impact on the behavior of afforestation, which indicates that afforestation is more under the leadership of the government. To realize the goal of ecological protection, it is recommended to make full use of the short-term effects of policy instruments, highlight the role of the government, and optimize the combination of instruments.