Mullite coatings were fabricated by atmosphere plasma spraying (APS) at varying primary gas flow rates. The flattening behavior of deposited particles as well as microstructure, mechanical properties of mullite coatings were studied in relation to the critical plasma spraying parameter (CPSP). Moreover, the dry sliding friction and wear behavior of mullite coatings was also evaluated. Results show that at a primary gas flow rate of 40 L/min (referring to a CPSP of 562.5), the spraying powders exhibit high melting degree, spreading degree and deposition efficiency. More importantly, the resultant mullite coating has the best mechanical and tribological properties.