One distinguishing feature of low-porosity and low-permeability sandstones is the departure of their elastic proper-ties from general porous and permeable sands. This paper developed a rock physics model focusing on the developed cracks in tight sandstones and their effects on tight sand. Pores with fluids were added to the rock matrix by using effective media theory, and cracks with fluids were added by using anisotropic fluid substitution equations which were derived by combining Hudson model and anisotropic Gassmann's equations. The elastic modulus in tight sandstones were then calculated with dif-ferent crack properties, such as crack density, crack shape, fluid content, and so on. The accuracy of the parameters esti-mation method was discussed based on rock physics model considering micro cracks. P-wave and S-wave velocities were esti-mated with the proposed modeling method. The accuracy and advantage of the model are verified by comparing with the real logging data. Thomsen parameters of fracture reservoir are extracted and can be used to indicate the cracks in reservoirs.%针对致密砂岩储层低孔低渗及微裂缝发育的特点，提出一种适合致密孔隙裂缝型储层的岩石物理模型构建方法：首先，在岩石基质中利用有效介质理论添加含流体孔隙，然后利用结合Hudson理论和各向异性Gassmann理论推导得到的各向异性流体替代方程添加含流体裂缝。基于构建的岩石物理模型，定量分析裂缝密度、裂缝形状、充填流体等储层岩石的物理性质对饱含流体岩石的纵横波速度的影响。采用某研究区实际井资料对该方法进行试算，完成纵横波速度的估算和裂缝储层各向异性参数的提取，纵横波速度的估算值与其实测值的吻合程度较高，且各向异性参数能够较好地反映裂缝发育位置，证明了本文方法的有效性。
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