This study aimed to identify the level of quality of the methods of school management supervision and its relationship to the quality of the performance of public-school principals in Muscat Governorate in the Sultanate of Oman from the point of view of school principals. The researcher used the correlation method and used a questionnaire including 71 items which consist of three parts: the first one deals with the demographic data respondents, the second part deals with the school management supervision which consists of (39) items divided into six areas, and the third part deals with the issue of administrative performance of school principals and consists of (32) items divided into five areas. After conducting the validity and reliability of the questionnaire tool it was distributed to the sample of the study, the sample included all principals of public schools in the Governorate of Muscat, who were estimated as (177) male and female, according to the annual statistics book issued by the Ministry of Education for the academic year 2021-2022. The study found a numbers of results. The most imported over are as follows: - The level of quality of school management supervision methods in public schools. from the point of view of government school principals, was high. - It also found that there were statistically significant differences due to the variables of the educational stage, while there were no statistically significant differences due to the variable of gender and years of administrative experience. - It also showed that the performance of the government school principals in the Governorate of Muscat was at a significant level, while there were no statistically significant differences due to the variables of gender, educational level, and years of administrative experience. Moreover, the study revealed that there is a statistically significant positive correlation between the level of quality of school management supervision methods and quality level of performance of the principals of government schools in Muscat Governorate. Based on; the study made a set of recommendations; the most important of which is that the Department of School Supervision at the Directorate General of Education in Muscal Governorate shall seek to develop the skills of school management supervisors, train them to effectively use modern supervisory methods, especially the electronic supervision method, the method of seminars, and to develop them professionally in how to determining and choosing the appropriate supervisory methods according to the nature of the objectives to be achieved and by keeping pace with the digital developments and quality standards.