An expanding model of the confinement of non-ideal detonation of small charge is established on the basis of the nozzle theory. Making use of the expanding model, the analytic relationship of small charge detonation velocity and the semi-empirical relationship of detonation pressure that both change with charge diameter and confinement condition are established. The detonation velocity and pressure of small charges are calculated and experimentally verified, and the detonation velocity deviation is less than 7% while the detonation pressure deviation is less than 9%.