This paper presents the theoretical modeling and parameter analysis of vibration assisted robotic assembly involving peg-in-hole insertion. Transitions among various mating configurations during the vibration assisted insertion are studied. Mating forces and insertion motions are analyzed and numerically simulated. Insertion failure is classified into several types, with the characteristic of each type studied. The types of insertion failure include jamming due to insufficient assembly forces, jamming due to robot deflection, jamming due to assembly geometry restriction, wedging due to compression forces, and peg sliding opposite to the insertion direction. Experiments are performed, where vibration is applied to the hole piece when a SCARA robot is performing peg-in-hole insertion, to verify the analytical results.