Abstract: The performance of drilling bits is mainly evaluated by means of the rate of penetration (ROP) and the bottom hole WOB (weight on bit) is the main parameter influencing ROP.And especially for horizontal wells, it is quite important to calculate and measure the actual bottom hole WOB because the friction drag of horizontal section is high and it is not easy to apply the load on the bit, which leads to larger difference between bottom hole WOB and ground WOB.The torque and drag model was established by combining Johancsik model Aadnoy 3D model together.The stiffness of pipe string is taken into account.The calculation of bottom hole WOB was divided into two steps.After the friction coefficient between drilling string and borehole wall was calculated by using the idling data of drilling bit, the bottom hole WOB in the process of well drilling was predicted based on the calculated friction coefficient.Meanwhile, the calculation program for bottom hole WOB was developed by means of C# in the integrated development setting of Visual C++ 2013.And then this newly developed program was used to calculate friction coefficient and bottom hole WOB.It is shown that the calculated bottom hole WOB is consistent with the measured one in terms of numerical value and variation trend.It is indicated that the WOB calculation model and program can predict the bottom hole WOB accurately based on ground drilling data.Bottom hole WOB calcula-tion model and program are applicable to post drilling analysis and can control the bottom hole WOB accurately by integrating with the conventional automatic driller, so as to improve bit performance and drilling efficiency and cut down drilling cost.