In the development of technology and industry, steel is one important materials, as evidenced by common use in the world manufacturing, maritime, building materials, piping, oil and gas. Therefore, it is important to study and optimize welding process parameters to improve quality joints and minimize defects. This study aims find various combinations MIG (Metal Inert Gas) process parameters for steel welding with variations current strength and coolant. The research method to carry out MIG (Metal Inert Gas) welding process and then conduct particle magnetic and macrostructure testing. The conclusion best particle magnetic test results (minimal defects) specimen 5 with parameters 100 Ampere and air cooling and worst result specimen 6 with parameters 100 Ampere and oil cooling and best macrostructure test results are specimen 8 with parameters 120 Ampere and air cooling and worst result is specimen 9 with parameters 120 Ampere and oil cooling.