[zhubo]

Recently, I found a reaction, but there were two products. I guess there may be two mechanisms, one radical mechanism, the other 1,3-dipolar mechanism. I wonder how to suppress the product through the 1,3-dipolar mechanism. Any input is appreciated.

[bontempo]

Could you give just a little bit more information? We won't steal your reaction... 

From what you've said, it seems that you should try and shut down mechanistic pathways involving charged/polarised species. One of the easiest ways to (try) to do so is a change of solvent. Try something less polar with a lower dieletric constant. But since we don't know which solvent you're actually using..
Also, you might want to repeat the reaction adding some ditert-butylphenol as a radical trap. If you obtain only (or mainly) the dipolar cycloaddition product, that gives some assurance as to the radical nature of the process leading to your "new" product.

[zhubo]

bontempo, thank you!
Chlorobenzene was the solvent used in my reaction. Could you give some more suggestion about the solvent which should be used in the reaction?