After 'VariantFiltration', variants supposed to be filtered still remained in the filtered vcf file.
How can I distinguish them? Which column in the vcf file should I look into?
You can look at the FILTER column. It should have a PASS for variants that passed. The variants that failed will have the name(s) of the filter(s) they failed.
If you applied FORMAT level filters using -G_filter, have a look at the FT annotation. It will either say PASS or the name(s) of the filter(s) it did not pass.