Free volume theory, which is a popular approach to solve the problems associated with glass transition in polymers, is applied to investigate multi-shape memory effect (multi-SME) of amorphous shape memory polymers (SMPs) as well. To understand the phenomena of multiple shape recovery behaviors, theories about the SME and multi-SME in amorphous SMPs are firstly developed. The thermodynamics in the SMPs with dual- and triple-SME is then investigated in the frameworks of the free volume model and Eyring equation, taking account of the dependencies of free volume and activation energy on relaxation time. Finally, the proposed free volume model is evaluated and compared with results from the amorphous SMPs with dual- and triple-SMEs. Results from our newly proposed model show a good agreement with experimental results obtained at different temperatures.