With the application of composite materials in the defense industry, the straightness measurement of composite material barrel becomes an technical issue that needs to be solved urgently. Traditional equipment used for steel pipe straightness measurement causes larger errors in composite material barrel straightness measurement. Therefore, finite element analysis software ABAQUS is used to analyze the composite material barrel deformation under different load and different supporting conditions. The three-dimensional finite element model of the composite material barrel is established. The deformation of composite material barrel caused by different weight measuring equipment under different supporting conditions of composite material barrel is obtained. Corresponding test is designed to prove the validity of the finite element analysis results. It is proved that the weight of equipment and the different supporting conditions oif barrel have significant influence on the composite material barrel straightness measurement accuracy. Therefore we can reduce the influence of test equipment weight by changing the different supporting conditions of barrel. The relationship between barrel deformation and test equipment weight is obtained by using the method of data fitting, and it provides theoretical basis for the design of straightness measurement system of composite material barrel.