Abstract: The operation mode of “well factory” achieves the benefit development of unconventional oil and gas. In this paper, the constituent elements of well-factory drilling cost were determined by analyzing the characteristics of the “well-factory” drilling of unconventional oil and gas, and these elements were quantitatively studied. Then, a well-factory drilling cost analysis model was established according to well-factory drilling process integration. The factors influencing well-factory drilling cost were determined and optimized. An optimization algorithm of well-factory drilling cost was developed. Several factors were mainly considered, including position and number of pads, drilling sequence, drilling learning efficiency, well type, wellbore trajectory, batch drilling sequence and drilling fluid recycling rate. Based on the practical drilling engineering in the tight oil reservoirs of Jiyang Depression, the Bohai Bay Basin, the model parameters were optimized. The optimal scheme was worked out by taking the cost minimization as the objective function, and the percentage of each drilling cost element in the optimal scheme was calculated. Rig cost (40.55%), casing cost (15.11%), drilling fluid cost (14.80%) and cementing cost (9.89%) are the top four cost elements, whose sum accounts more than 80% of total well-factory drilling cost. Finally, the credibility of the cost calculation model was evaluated by using the “cosine similarity” method, and its error is less than 2%. This research provide theoretical basis for the optimized design and cost estimate of well-factory drilling scheme of unconventional oil and gas.