The meaning of 1. symbol: The symbol is used to indicate whether a number is positive or negative. For junior high school students, it may be difficult for them to understand why a number can be positive or negative, and the function and significance of symbols.

2. The concept of absolute value: absolute value is the distance of a number from 0, which is represented by the absolute value symbol |. Junior high school students may be confused about why the absolute value of a number can be positive or negative, and how to calculate the absolute value of a number.

3. Comparison of positive and negative numbers: Junior high school students may encounter some problems about the comparison of positive and negative numbers, such as comparing the sizes of two negative numbers, or comparing the sizes of a positive number and a negative number. These problems may require them to solve with some skills and rules, which may be difficult for beginners.

4. Operation of positive and negative numbers: Junior high school students may encounter some difficulties in learning the operation of positive and negative numbers. For example, they may wonder why positive numbers plus positive numbers are still positive, while negative numbers plus positive numbers are negative. In addition, they may encounter some problems about multiplication and division of positive and negative numbers, which require them to understand and master the corresponding laws and properties.

In short, junior high school students may encounter some difficult knowledge points when learning the concept of positive and negative numbers, including the meaning of positive and negative symbols, the concept of absolute value, the comparison and operation of positive and negative numbers, etc. These knowledge points need students to deepen their understanding through examples and exercises, and gradually master the relevant laws and properties.