Legal analysis: Stealing underwear is illegal. If the theft is frequent, the amount is large and the circumstances are serious, it will generally be detained for more than 10 and less than 15. If its property is valuable, criminal responsibility will be investigated according to law. According to the laws of our country, whoever steals public or private property in a large amount, or steals it for many times, shall be sentenced to fixed-term imprisonment of not more than three years, criminal detention or public surveillance, and shall also or only be fined.

Legal basis: Article 49 of the Law of People's Republic of China (PRC) on Public Security Administration Punishment, whoever steals, swindles, robs, extorts or intentionally damages public or private property shall be detained for more than five days and less than ten days, and may also be fined less than 500 yuan; If the circumstances are serious, he shall be detained for more than 10 and less than 15, and may also be fined less than 1000 yuan.