Aluminum and its alloys are widely used in aircraft automotive and in construction industries because of their desirable physical properties. Positron annihilation lifetime technique (PALT) is non-intrusive method, which is used extensively in materials science. The positron annihilation lifetime spectra were measured for plastically deformed Al-3004 samples at different degrees of deformation up to 25% using hydraulic press at room temperature. Plastic deformation basically produces dislocation defects. Saturation trapping of positron in defect states starts at 6% thickness reduction at which the positron annihilation lifetime of about $215 \pm 5\ \text{ps}$ was obtained. The two-state trapping model of positrons after fitting with the experimental measured positron lifetime data was used to calculate the concentration of dislocations which are used in determination of the stored dislocation energy at different degree of deformation. The variation of the stored dislocation energy with thickness reduction seems to be an exponential growth, reaches its maximum value of $6.8\ \text{KJ/m}^3$ at 6% thickness reduction according to the increasing of the dislocation density as predicted theoretically.