The effect of defects in metal Ti such as vacancies, self-interstitial atoms and impurity He atoms on mechanical properties of metal Ti sample was studied using molecular dynamics simulation. First, the stress-strain curves of perfect Ti sample at different strain rates were calculated. The results show that the stretching process can roughly be divided into three stages, elastic deformation, plastic deformation and fracturing. For comparison the stress-strain curves of metal Ti samples with vacancies, self-interstitial atoms and impurity He atoms were researched, respectively, in which the strain rate was set as 2×10⁹ s^-1. Finally the corresponding Young's moduli were calculated. It is found that after carefully investigating that the mechanical properties of metal Ti are degraded by each of these effects in it and the degradation degree increases with increasing defect concentration. However, the stretching process of samples is not essentially affected by these effects (the stress-strain curves of Ti samples with defects have still 3 stages). In this process, self-interstitial atoms in samples always exist for they to be bonded by metal Ti atoms, but impurity He atoms in samples are released due to their extraordinarily low solution in metal Ti.