Solar system converts solar energy into usable energy form. Total energy gain depends on the total amount of radiation that strikes radiation collecting surface and this amount depends strongly on tilt angle. In the present study, the radiation collecting surface tilt angle was studied through two approach of study. First approach through getting the tilt angle of fully tracking solar system and then developed best tilt angle yearly and seasonally. Second approach depends on getting the evaluating the total solar radiation incident on surface tilt by certain angle then evaluating best angle. The first approach results show that tilt angle for latitudes from equator up to Cancer tropic is not equal to latitude angle while it approximately equal to latitude angle for latitudes started from Cancer tropic this is for one yearly fixed tilt angle. A correlation, for yearly best tilt angle as a function of latitude angle, was presented for both two cases single tilt angle and two tilt angles through year and a comparison between them was done. For latitudes next to Cancer tropic, the results showed that the value of enhancement, when using two tilt angles per year, may reach to 7.11% more than using single tilt angle per year and this value is directly proportional with latitude angle. Finally, using two tilt angles per year is more convenient. Results from first approach compared with data from second approach. Data extracted from other references are also compared with results of the two present approaches.