The relationship among mechanization services,labor structure change and farm efficiency remains one of the most persistent debates in the agricultural production field. Based on the farm level pooled cross-section data from China Labor-force Dynamics Survey (CLDS) in 2014 and 2016,we apply a translog Stochastic Frontier Model to the estimate of the technical efficiency (TE) in food crop production and the construction of a mediation model to analyze the causal relationship among mechanization services,rural labor structure change and technical efficiency. We find that:i) mechanization services and labor transferring to service sector have significantly positive effects on TE,while labor loss in agriculture and labor transferring to industry sector have negative effects on TE in food crop production. No evidence was found that the feminizing of labor has negative impact on TE; ii) mechanization services have a significant mediation effect on the impact of labor structure change on TE,and labor loss in agriculture,feminizing of labor,labor force transferring to industry and service sector have positive effects on mechanization services,which improved the TE; iii) the use of mechanization services leads to labor transferring to industry sector,which has a significant mediation effect on the positive effects of mechanization service on TE and also causes labor loss,feminizing and accelerates labor transferring to service sector. The results suggest that mechanization services could lift the technical efficiency,but it is necessary to deal with the negative mediated effects of labor structure change on farm efficiency in food crops production.