Agricultural socialized service as an inevitable product of agricultural division and a mediator of element effective allocation, plays a critical role in agricultural modernization. This paper, based on 134 cases of “entire mechanization + comprehensive agricultural affairs” nationwide, combined with in-situ investigation data of comprehensive agricultural affairs in H city’s L district, J city’s W district, Zhejiang province, uses rooting theory and NVivo12 software for data coding and analysis, and constructs an agricultural socialized service system model to study the mechanism, dynamics and challenges of its promotion on industrial upgrade. Agricultural socialized service system is composed of two key categories, production supporting service and factor intensive service, covering 10 major categories and 35 categories. Production supporting service boosts marginal benefits from increasing production efficiency, decreasing costs and optimizing resources allocation; while factor intensive service uses professionalintermediate inputs to promote human capital development and innovation through technical advances, digitalization andbrand marketing. Agricultural socialized service further optimizes process connection and benefits connection so as to raise overall agricultural competitiveness and marginal benefits of industrial chain. Five drives including market leading, enterprise consolidation, technical supports, policy supports and local connection jointly promote agricultural socialized service and industrial upgrade; however, agricultural socialized service faces such difficulties as low industrial added values and shortage of agricultural talents. This paper presents suggestions on promoting policy standardization, accelerating agricultural technical conversion and cultivating agricultural talents for high quality agricultural socialized service.