Analyzing the influence mechanism of the transformation of demand willingness and behavior of forestry social services (FSS) of farmers with different operation scales in the production process is crucial for promoting the modernization of the collective FSS system. Based on the survey data of 800 farmers in 3 provinces of China, this study uses the multivariate (Mv-) probit model to quantitatively analyze the mechanism of factor endowments’ influence on farmers’ deviation of demand willingness and choice behavior on three FSSs in the different scales: fine seed and cultivation technology service (SCTS), forest insect pest prevention and treatment service (IPTS), and timber collection and sale service (TCSS). Our results show that the demand rates of IPTS, SCTS, and TCSS are 80.25%, 68.00%, and 68.38%, respectively. Large-scale farmers are more willing to demand FSS than small and medium-scale farmers. However, their actual adoption behavior is low, and there are significant deviations in farmers’ demand willingness and adoption behavior for different types of FSS, i.e., 30.37%,12.62%, and 44.88% for SCTS, IPTS, and TCSS, respectively. Farmers’ transformation from demand willingness to adoption behavior is significantly affected by farmers’ characteristics. Compared with the farmers’ demand willingness model, the inhibitory factors for the transformation behavior for FSS increased significantly, including common factors such as the scale of the managed forest land, the difficulty in applying for logging permits, getting afforestation subsidies, and the proportion of forestry income. In contrast, these factors had the opposite influence on the demand willingness model. The number and degree of positive significant influencing factors decreased, with only the family labor force positively influencing farmers’ transformation behavior for SCTS. Based on the results, it is suggested to scientifically guide the orderly flow of rural labor, promoting the moderate scale concentration of forest land flow, accelerating the speed and benefits of inclusiveness in rural finance, and resolving issues related to farmers’ loans to improve the adoption behavior of FSS by farmers.