To improve the overall capability of mud pump, the stress distributions of pump body was analyzed, and the pump case structure was optimized. The three-dimensional finite element method was adopted to analyses the stress and strain on 1600HP mud pump case, based on the 1800HP mud pump maximum load conditions. The preliminary analysis showed that the stress concentration locate in the front connecting plate and the side plate, which didn’t meet the material strength. The pump case was optimized to meet the required 1800HP condition according to the results of analysis. Without increasement of the total volume and total weight, the mud pump’s power grade was improved. The optimized mud pump can meet the conditions from 1600HP to 1800HP. Not only suit the change of drilling depth, lifting equipment and auxiliary pipe network equipment are not replaced, the cost of land rig is reduced greatly, the economic benefit is improved.