Abstract: In this paper, the relationship between plant industry mechanization degree and labor demand was proposed and researched. To improve agricultural mechanization theory and provide theoretical reference of scientifically estimate the quantities of the labor force in planting industry and surplus labor. The linear alternative relationship was pointed out while replacing farming workforce with farming machine units with the same type, the separability of mechanization degree was also proposed and proved in this paper. A model of relations between the farming mechanization degree and labor demand was established. The simulation results of the model show that it's not only the current amount of labor demand in a particular area that could be calculated, but also the amount of labor demand in the various moment in future could be calculated through forecasting mechanization degree and sown areas for the variety of crops in the future. Finally, an example was presented for demonstration purposes.