Abstract: In this study, numerical simulation and investigation of different radiation models on the triangular solar collector have been initially addressed. In this study, the effect of the change in the bottom wall temperature, an apex angle of 40°, the temperature changes of the lateral walls of the triangle, various types of radiation models in the steady and transient states and also the impact of changes in the Grash of number, Nusselt number and heat transfer coefficient on the performance of the collector and contours of temperature, pressure and speed in the steady state have been investigated. By doing the above activities, the obtained results are listed as follows. In all states, two separate flows are generated inside the chamber as a result of temperature difference between the walls and the bottom surface. Heat transfer coefficient has a minimum value in the middle of the wall. The reason is the existence of the stagnation point and the minimum speed at this point. The amount of heat transfer decreases from the left and right edges towards the middle of the absorbent. Speed changes of the bottom wall of the absorbent reach from a maximum value in both left and right walls to a minimum value in the middle. Pressure also has a maximum amount on both right and left sides and in the middle part which is the stagnation point, we will have a minimal amount of pressure. The heat flux in the transient state is not fixed in the bottom and has a maximum value in the middle and respectively decreases to the left and right walls. The behavior of changes in pressure and speed in the transient state is similar to the steady state. In the transient state, the Nusselt number is reduced from the beginning of the analysis time by increasing the time steps until after 8 sec, the changes of the Nusselt number reach their minimum amount and then, it remains constant. In the transient state, static and dynamic pressures and speed rate increase with the increasing of the time step.