Selective laser melting (SLM) technology is widely used in the additive manufacturing of three-dimensional complex parts, but due to the instantaneous high temperature of the laser, it is easy to generate thermal stress on the parts and affect the processing quality. In this paper, a Ti6Al4V three-dimensional finite element simulation model is established, and the SLM deposition forming process is simulated to explore the influence of the inter layer idle time of the double-layer multi-channel deposition model on the temperature distribution and thermal stress evolution. The results show that the simulated molten pool is in good agreement with the experimental results, which verifies the accuracy of the model. After the first layer is deposited, from the surface temperature distribution the cooling effect is remarkable. The increase of the idle time makes the heat conduction conditions better. After cooling, the X-direction stress presents a "sawtooth" distribution, and the maximum stress appears at the lap joint. As the inter layer idle time increases from no stay to 60s, the X-direction stress gradually decreases, maximum drop of 30%; the Y-direction stress presents a "Convex" and "Concave" distribution. The residual stress is distributed in a "Stripe" along the scanning direction; the maximum stress of the top path in the Y-direction first increases and then decreases, and the stresses of the Middle and Bottom paths show a decreasing trend. Therefore, appropriate inter layer idle time can stabilize the heat conduction, effectively reduce the residual stress after cooling.