Abstract: According to IMO “International Code for the Construction and Equipment of Ships Carrying Liquefied Gases in Bulk” and the relevant regulations for pressure containers,“GB150.3-2011”,a 3-dimensional method for the calculation of internal pressure of Type C independent tanks of miniature LNG carrier is given in this paper. With the assistance of the modeling and calculating function of AutoCAD,the VBA secondary development is used to achieve the 3-dimensional calculational of the internal pressure and thickness of plates. Also,the internal pressure of a Type C independent tank is calculated with both the 3-dimensional method and traditional 2-dimensional method separately,and the obtained results are compared carefully. Meanwhile,the influence of the acceleration caused by ship motion on the results is analyzed. It is shown that the 3-dimensional method yields more accurate results and it is preferable in the precision design. However,in real projects,the traditional 2-dimensional method is also applicable in the internal pressure calculation of single-cylinder Type C independent tanks of a design steam pressure over 0.3 MPa in general,and the influence of the acceleration caused by ship motion cannot be ignored. The 3-dimensional method should be taken for the internal pressure calculation in the tanks of other types in lower design steam pressure.