This paper describes a new positioning method that improves the availability and accuracy of Multi-global navigation satellites system (GNSS) positioning by using QZSS satellites in urban canyon environments. Standard multi-GNSS is problematic because one satellite is defined as the master satellite in each GNSS, leaving insufficient numbers of satellites for positioning roles. Our new method uses QZSS as the sole master satellite. To this end, we solve the ambiguity of QZSS by the wide- lane method and the QZSS LEX signal, and preserve that double-difference (DD) ambiguity is integral number. We also estimate the inter system bias (ISB). The GNSS used in our method includes GPS, QZSS, GLONASS, Galileo, and BeiDou satellites. Static evaluation tests were conducted in open-sky and narrow-sky environments. The open-sky evaluation confirmed the accurate positioning ability of our proposed method (horizontal RMS error: 1.6 cm), whereas the narrow-sky evaluation confirmed that our proposed method operates with accurate positioning and high availability in urban canyon environments (fixed ratio: 92.7%, horizontal RMS error: 4.2 cm). In conclusion, our method realizes high accuracy and availability high-coverage positioning.