Abstract: Outsourcing agricultural machinery services is an important part of the agricultural socialization service system, which is related to the development of agricultural mechanization and the organic connection between small farmers and modern agriculture. Based on the large national sample data CLDS2016, this paper studied the impact of farmland management scale on rural households’ outsourcing agricultural machinery services and explored the moderating effect of land ownership stability by the Ordered Probit model. Results show that: 1) small-scale rural economy is still relatively common, but the promotion of agricultural machinery outsourcing services has made some progress and agricultural scale operations can be increased through service scale operations; 2) there is an inverted U-shaped curve relationship between the scale of farmland management and farmer’s agricultural machinery service outsourcing, with an inflection point of 2.833 hm2. Farmers’ agricultural machinery service outsourcing behaviors of different farmland management scales are different; 3) farmland adjustment has a negative moderating effect and compared with farmland adjustment, when there is no farmland adjustment (land rights are stable), the inflection point of the curve between the scale of agricultural land and outsourcing agricultural machinery services is shifted to the left by 2.011 hm2; and 4) farmland title confirmation shifts the inflection point of the curve to the left by 0.709 hm2, but the adjustment effect is not significant. The reason might be that the policy effect of the confirmation of farmland ownership is lagging behind. Therefore, this paper suggests to comprehensively consider regional differences and the diverse needs of agricultural production when developing agricultural machinery outsourcing service market, to improve the service quality of agricultural machinery outsourcing, to standardize market operations, to improve the supporting system of farmland right confirmation policies, and to establish farmland data exchange platform.