According to Mori's program, varieties covered by rational curves are built up from anti-canonically polarized varieties, aka Fano varieties. After fixed the dimension and singularity type, Fano varieties form a bounded family by Birkar's proof (2016) of Borisov-Alexeev-Borisov conjecture, which In particular implies that the anti canonical volume -K^\dim is bounded. In this talk, we focus on canonical Fano threefolds, where boundedness was established by Koll\'ar-Miyaoka-Mori-Takagi (2000). Our aim is to find an effective bound of the anticanonical volume -K^3, which is not explicit either from the work of Koll\'ar-Miyaoka-Mori-Takagi or Birkar. We will discuss some effectiveness results related to this problem and prove that -K_X^3\leq 72 if \rho(X)\leq 2. This partially extends early work of Mori, Mukai, Y. Prokhorov, et al.