Siliceous dolomite in Mao2 Member of Maokou Formation has strong heterogeneous pore structure in central Sichuan Basin. The off-white silicalite with developed diffuse pores shows abnormal nuclear magnetic resonance (NMR) response features where pore size does not match T2 relaxation time. This brings difficulties to the effectiveness evaluation of dolomite reservoirs. Taking off-white silicalite from siliceous dolomite reservoirs in the upper Mao2 Member of Maokou Formation in central Sichuan Basin as research objects. With high-precision CT scanning, scanning electron microscopy and NMR physical experiments, a standard pore-throat theoretical model and a pore cluster model based on real cores and Numerical simulation of NMR response are constructed. The influence rules of pore connectivity, mineral surface relaxation coefficient, rock magnetic susceptibility and echo interval on NMR T2 spectrums are analyzed. The results indicate that the special pore structure of off-white silicalite serves as the primary cause for the abnormally high T2 values in the NMR response of off-white silicalite in Maokou Formation. The pore cluster connectivity of off-white silicalite dominates the NMR response. As the throat diameter decreases, the peak position of the T2 spectrum shifts left gradually. After the throat diameter is reduced to the critical value, the influence of connectivity on the response decreases significantly. Mineral surface relaxation coefficient, rock magnetic susceptibility and echo interval are not the causes of the abnormally high T2 values in the NMR response of off-white silicalite in Maokou Formation. Under the same research conditions, the surface relaxation coefficient of silicalite is higher than that of limestone and dolomite. Compared with igneous rocks, the magnetic susceptibility of silicalite is close to that of dolomite. The internal gradient magnetic field inside silicalite remains low and cannot lead to an increase in T2 values. It is clarified that the blocky distributed diffuse pores inside off-white silicalite with excellent internal pore connectivity with each single diffuse pore cluster trigger abnormal NMR responses of off-white silicalite in Maokou Formation in central Sichuan Basin. This finding provides theoretical support for NMR logging analysis and reservoir effectiveness evaluation of siliceous dolomite reservoirs.