Hi Minghao,
thanks for reaching out. I just tried a crossmatch on our web x-match service, with 50 sources from the LS DR 7 footprint, against ls_dr7.tractor table; it worked fine (and very fast). Could you please provide more information, i.e. show here the first few rows (and the header line) of your own table, and tell which selections and options you have clicked in the web x-match service?
Thank you,
Robert