依我看，你原来的管子是PEX-A的，新买的是PVC的，不一样的管子，中间要加个这样的接头

https://www.homedepot.com/p/Apollo-3-4-in-Brass-PEX-A-Barb-x-3-4-in-Schedule-40-PVC-Straight-Adapter-EPXPVC34/305469324?source=shoppingads&locale=en-US&pla&mtc=SHOPPING-BF-CDP-GGL-D26P-026_001_PIPE_FITTING-NA-NA-NA-PMAX-NA-NA-NA-NA-NBR-NA-NA-NEW-_PMAXTEST&cm_mmc=SHOPPING-BF-CDP-GGL-D26P-026_001_PIPE_FITTING-NA-NA-NA-PMAX-NA-NA-NA-NA-NBR-NA-NA-NEW-_PMAXTEST-17697557984--&gclsrc=aw.ds&gad_source=1&gad_campaignid=17687574624&gbraid=0AAAAADq61UcVvHO3MiXEVA7dibC1YWce1&gclid=CjwKCAjwhuHEBhBHEiwAZrvdcoZ8R2lu6JPoxfhEDRvKqaMLfHMKxMTWgVrZM0yUNs5d4Fps7dOl1RoCrQ8QAvD_BwE