In response to the substantial expenses, significant disruptions, and considerable environmental impact resulting from order fulfillment on online platforms, a joint optimization model for order splitting and consolidation delivery was developed based on the “divide and conquer” principle. The model aims to minimize costs by fully leveraging multi-warehouse resources and consolidating deliveries at distribution centers. The innovative aspects of the model include: firstly, considering both quantity splitting and category splitting scenarios; secondly, establishing more realistic order dispatch time constraints; and thirdly, jointly optimizing order splitting and consolidation delivery. Through the application of fuzzy set theory, the fuzzy programming model is transformed clearly and impartially. Through case studies, the feasibility of the model has been verified. The experimental results show that compared with the existing models, the proposed model has more advantages in controlling order fulfillment costs, reducing customer disturbances and reducing environmental pollution. At the same time, the sensitivity analysis shows that the order fulfillment cost is positively correlated with the number of categories and negatively correlated with the inventory.