Stress concentration is the key factor which induces the damage of oil-gas pipeline. It brings the risk to the safety of pipeline. Point at online stress testing and risk evaluation,weak magnetism stress internal testing technology is put forward. The reason for formation of weak magnetic signal is analyzed. The weak magnetic effect of ferromagnetic material under different stress is simulated by simulation software which is based on first principle. Twice weak magnetism stress internal testing method under different run pressures is put forward. Risk evaluation method of oil-gas pipeline stress concentration is provided. Highly sensitive weak magnetism stress internal testing equipment which is independently researched and developed is applied in actual pipeline. Online internal testing and risk evaluation of the long distance pipeline are achieved. The testing result is validated through different testing method. The results show that the formation of weak magnetic signal is related to stress and stress damage. Stress induces atomic magnetic moment change. Weak magnetic signal change with stress macroscopically. Twice weak magnetism stress internal testing method under different run pressures can accurately evaluate stress concentration risk level of pipeline. Actual engineering application and excavation testing results indicate that weak magnetism stress internal testing technology is feasible and effective.