TiNi　tubes　with　various　sizes　and　boundary　constraints　subjected　to　radial　quasi-static　compression　were　systematically　studied.　The　contour　curves　of　the　tubes　were　extracted　from　the　real-time　charge-coupled　device　(CCD)　images,　and　the　circumferential　strain,　bending　moment,　and　phase　composition　distribution　were　calculated　based　on　the　contour　curves　and　some　assumptions.　It　was　found　that　the　load-displacement　curves　had　hysteretic　loops,　and　all　specimens　could　recover　to　their　initial　shape　after　unloading,　which　was　attributed　to　the　effects　of　austenite-martensite　phase　transformation　and　phase　transformation　hinges　(THs).　For　single-tube　experiments,　the　numbers　of　TH　were　observed　to　be　twice　the　numbers　of　constraints.　For　vertical　double-tube　experiments,　the　main　deformation　of　each　tube　was　concentrated　on　its　upper　half　circle.　The　energy　dissipation　rate　(EDR)　and　the　dissipated　specific　energy　(SE)　in　single-tube　case　increased　with　decrease　of　the　diameter-wall　thickness　ratio　(DTR;　D/t)　or　increase　of　the　constraint　number.　With　a　four-directional　constraint　condition　and　same　D/t,　the　EDR　and　SE　of　vertical　double　tubes　were　greater　than　that　of　a　single　tube　and　close-packed　seven　tubes.　The　present　results　could　give　a　reference　for　designing　repeatedly　used　shock-resistant　element　with　higher　energy　absorption　capacity.