Qingming is a lunar festival, but why can we meet April 3, 4 and 5 of the solar calendar every time?

There are many basic concepts in your question that must be clear in order to understand the uniqueness of this calendar in China, that is, the beginning of the year, the lunar calendar, the solar calendar, the combined calendar of yin and yang, and the solar terms.

Year of Lunar New Year: the first day of the year. Since Yao Shun, China has regarded the Lunar New Year as Spring Festival or New Year's Day. Although the calendar is changeable in history, it always falls in the year of the Lunar New Year, and it is the same today, but it is not the first day of the Lunar New Year in beginning of spring solar terms.

Lunar calendar: A calendar based on the lunar cycle of 29.5306 days.

Gregorian calendar: A calendar based on the earth's 365.2422-day orbit around the sun.

Lunar calendar: The lunar calendar in China is defined by solar terms based on the earth's orbit around the sun, and the moon's orbit is defined on the basis of solar terms, which is used to adjust the moon's orbit to produce a "leap moon".

Solar terms: The earth's orbit around the sun is 360 degrees (pi), which is divided into 24 parts. Every 15 degree, a point is 24 solar terms. However, the earth's orbit around the sun is not 360 days, but 365.2422 days, that is, a solar term has 15.2 18 days, so the time of the sacrifice can be accurate to "seconds", and the day of the sacrifice is not the same moment. It is not enough for Tomb-Sweeping Day to appear one or two days after the solar term and the lunar calendar.

The lunar calendar takes 12 months as a year, ***354 days or 355 days, which is about 1 1 day different from the earth's orbit around the sun. Therefore, coordination is achieved by adding leap months (the period of leap is about 19 years and 7 leap months). The year with leap month is 13 months, and the whole year is about 384 days. Therefore, the "beginning of spring" solar terms set by the sun and the "beginning of spring" solar terms set by the moon cannot have a relatively fixed date with the Gregorian calendar date!