For the ancients, the Euclidean axiom system was a desirable model for deductive system building. Avicenna used this model to construct a metaphysical propositional system. However, some have ruled out the possibility of constructing such a system for metaphysics and have considered the attempt to construct such a system to be a mistake. The issue that this article has tackled is posed in the form of the question of how and under what possibility did Avicenna construct a deductive propositional system for metaphysics? This issue is of great importance and necessity in that it questions the conditions of possibility of the first deductive propositional system of metaphysics. In order to answer this question, the present article first examines the structure of the propositional system of Avicenna's metaphysics with regard to its "components" and "order" in a descriptive-analytical manner, and then searches for the possible conditions for its realization. According to Avicenna's scientology, metaphysics based on the lemma method should only use conventional principles. However, metaphysics based on the immediate method also has the possibility of using axioms. According to Avicenna, metaphysics using the lemma method is possible in itself, but difficult in practice. This difficulty, on the one hand, and educational purposes, on the other hand, have caused Avicenna to resort to the immediate method in addition to the lemma method; and thus, to form a "conventional principle-subjective principle" structure. The results of the article show that the structuring of Avicenna's propositional system of metaphysics is possible only within the combined framework of these two methods. And this combination is also possible based on the theory of issuance in ontology and the theory of knowledge in Ibn Sina's epistemology.