The importance of diagram system MnO2─NaVO3 is in obtaining a crystal phase (chemical compounds or solid solutions). Acknowledging the fact that these compounds have grade properties in the field of technology, it was important to study the possibility of obtaining new phases with different mole ratios, and to draw phase diagram for it, especially the used compounds in this study have different crystal structures. The samples were made beginning from powders of reagent grade MnO2 and NaVO3 of 5gr for each of them at following percentage mole ratios of MnO2: (10, 20, 25, 30, 33.33, 50, 66.66, 70, 71, 75, 80, 90). The mixing and grinding process was made for these samples. Then, it made pills ellipsoidal using manually hydraulic press, and it burned into oven at different degrees. The study was made using powder X─Rays diffraction PXRD and different thermal analysis TG─ DTA. The results are compared with X─rays spectrums of grade compounds and parameters of it. Then, the formation phase changes degrees were determined. New compound was formed at ratio (MnO2)10(NaVO3)90 mole%, and crystal solid solution was formed to ratio (MnO2)25(NaVO3)75 mole%. As well solid solution (amorphous+ new compound) was formed until mole ratio (MnO2)75(NaVO3)25 mole%, and amorphous solid solution was formed beginning mole ratio (MnO2)80(NaVO3)20 mole%, then the phase diagram for the studied system was drawing.