Based on ROCSAT-1 satellite observations from 2000 to 2003, this study uses a new method to identify plasma irregularities (plasma bubbles and plasma blobs) and their longitudinal ranges in low and middle latitude ionosphere. Furthermore, the distributions of longitudinal ranges of plasma irregularities are analyzed depending on local time, season, geographic longitude, and geographic latitude. The results show that, during different seasons, mesoscale plasma bubbles and plasma blobs (0.45°~°, about 50~1000 km) constitute over 90% of the plasma irregularities in low and middle latitude ionosphere, with longitudinal ranges primarily concentrated within 1° ~4°, exceeding more than 70% of the total irregularities. Moreover, plasma blobs and its longitude ranges exhibit noticeable variations with local time, geographical longitude and season. The peak occurrence time of plasma blobs is slightly delayed compared to that of plasma bubbles, occurring approximately one hour later. The occurrence frequency of plasma blobs is highest during the summer solstice (June solstice), primarily distributed in the -180°E to -100°E, -30°E to 60°E, and 90°E to 180°E longitude sectors. The second-highest occurrence is during winter solstice, predominantly appearing in the -180°E to 0°E longitude sectors. Additionally, plasma blobs occur preferentially in the winter hemisphere rather than in the summer hemisphere, and they also show a preferential occurrence in the autumn hemisphere compared to the spring hemisphere. Comparing the characteristics of plasma blob with that of plasma bubble, this study suggests a potential connection between plasma bubbles and plasma blobs, indicating that plasma blobs may appear with the evolution of plasma bubbles. Moreover, plasma blobs can also be generated and appear independently.