i find out that the jpg with a alpha channel after compressed with astc
Correct me if I am wrong, but if I understood correctly, you want to know how to compress a jpg file with no alpha channel to ASTC, with the final compressed ASTC file having alpha channel?
If that is the case, you can do it with PVRTexToolCLI:
PVRTexToolCLI -i test.jpg -f ASTC_4X4 -q astcveryfast -o test.ktx
Remember that in the current version of PVRTexToolCLI, you need to use a block size for ASTC that is an integer factor of the image dimensions. For instance, if you have an image with dimensions 640x800, you cannot use ASTC_6X6 since 640/6 = 106.67 and 800/6 = 133.33. Instead, you can use ASTC_4X4, since 640/4=160.0 and 800/4=200.0