We provide decompositions of symmetric Dirichlet forms into recurrent and transient parts as well as into conservative and dissipative parts, in the framework of \(\sigma \)-finite measure spaces. Combining both formulae, we write every Dirichlet form as the sum of a recurrent, dissipative, and transient-conservative Dirichlet forms. Besides, we prove that Mosco convergence preserves invariant sets and that a Dirichlet form shares the same invariants sets with its approximating Dirichlet forms \({\mathcal {E}}^{(t)}\) and \({\mathcal {E}}^{(\beta )}\). Finally, we show the equivalence between conservativeness (resp. dissipativity) of a Dirichlet form and the conservativeness (reps. dissipativity) of \({\mathcal {E}}^{(t)}\) and \({\mathcal {E}}^{(\beta )}\). The elaborated results are enlightened by some examples.

在\（\ sigma \）-有限度量空间的框架内，我们将对称Dirichlet形式分解为递归和瞬态部分，以及保守和耗散部分。结合这两个公式，我们将每个Dirichlet形式写为递归，耗散和瞬变保守Dirichlet形式的总和。此外，我们证明了Mosco收敛保留不变集，并且Dirichlet形式与其近似Dirichlet形式\（{\ mathcal {E}} ^ {（t）} \）和\（{\ mathcal {E }} ^ {（\ beta}} \）。最后，我们证明Dirichlet形式的保守性（分别为耗散性）与\（{\ mathcal {E}} ^ {（t）} \）的保守性（重复耗散性）相等，并且\（{\ mathcal {E}} ^ {（\ beta}} \）。详细的结果通过一些例子得到启发。