The project aims to study the mechanical properties of polyethylene (PE) at different strain rates in equal density and constant temperature conditions, and to improve the strain rate term of the original constitutive equation. The stress-strain curves of PE at different strain rates were measured with a universal material testing machine, and the variation trend of maximum tensile strength and elongation at break was studied with the increase of strain rate; Based on the Sherwood-Frost constitutive model, the power function term was added to Seeger model of classical thermal activation mechanism to realize the coupling of strain rate and strain; Based on the least square method, the parameters of the constitutive model were fitted with the software of Matlab, and the fitting results of the constitutive equation were compared with the experimental data at the rates of 300, 400, 500 mm/min. The fitting data of the improved constitutive model were more consistent with the experimental results. The maximum error was 8.12%, which occurred at the speed of 300 mm/min. With the increase of tensile rate, the maximum tensile strength of PE material increases gradually, while the elongation at break decreases gradually; after improving the strain rate term, the constitutive model has higher fitting accuracy and can provide accurate material parameters for finite element analysis.