In this work, the three species food chain models which are the simplest biological models with three trophic levels are investigated. After a non-dimensionless transformation, the model is transformed to a three first order ordinary differential equations with six parameters. The boundedness and positivity of solution with positive initial conditions are first established. Then we classify the existence and local stability of all boundary equilibria. Moreover, we obtain a complete classification of parameter space. For each region of the classification, the necessary and sufficient conditions of existence, non-existence and multiplicity of positive equilibria are obtained. However, the local stability of positive equilibrium is verified numerically. Finally, some numerical simulations are performed for each region of our classification.