To understand combustion characteristics of igniter in microscale tube,B/KNO₃ combustion in microscale tube were obtained from high-speed photography. Results show that wall heat loss and tube resistance are the main affecting factors for combustion stability. Combustion is stable in 1.0-2.0 mm quartz tube,and B/KNO₃ burning rate varies weakly. B/KNO₃ burning rate is proportional to combustion chamber pressure among 0.1-4 MPa,however,it is not consistent with exponent law. Combustion is unstable when the inner diameter of quartz tube is decreased to 0.5 mm,and the burning rate is increased with increasing of time. When the inner diameter of quartz tube is reduced further,breakdown phenomenon is produced and combustion quenching is caused. In addition,B/KNO₃ burning rate is in inverse proportion to wall thickness in the certain extent.