Let X be a metric space with doubling measure and L a non-negative self-adjoint operator on \(L^{2}\left( X\right) \) whose heat kernels satisfying the Gaussian estimates. Let \(\varphi : X \times [0, \infty ) \rightarrow [0, \infty )\) satisfy that \(\varphi (x, \cdot )\) is an Orlicz function for any given \(x \in X\) , and \(\varphi (\cdot , t)\) is a Muckenhoupt \({\mathbb {A}}_{\infty }\left( X\right) \) weight uniformly in \(t \in (0, \infty ).\) In this paper, we introduce the weak Musielak–Orlicz Hardy space \(W H_{L}^{\varphi }\left( X\right) ,\) associated to the operator L. And we obtain the atomic characterization of \(W H_{L}^{\varphi }\left( X\right) \) . Moreover, we establish non-tangential maximal functions characterizations of \({WH}_{L}^{\varphi }\left( X\right) \) via the atomic decomposition.