The second volume of the fourth grade mathematical knowledge tree can be drawn step by step according to the difficulties of mathematical knowledge points. The following are the suggested contents and drawing methods of the mathematical knowledge tree:

1. Understanding number: natural number, addition and subtraction, integer, number axis.

2. Application of numbers: understanding of length, volume and mass units, conversion between length units, conversion between area units and conversion between volume and mass units.

3. Understanding and application of fractions: basic concepts of fractions, comparison of fractions, conversion of fractions into simplest fractions, conversion of fractions into fractions with fractions, addition, subtraction, multiplication and division of fractions, spatial graphics and their expression, and application of fractions.

4. Understanding and application of decimals: basic concepts of decimals, comparison of decimal sizes, addition, subtraction, multiplication and division, and reciprocity of decimals and fractions.

The painting method is as follows:

1. Draw a big trunk according to "Understanding Numbers".

2. Draw two branches on both sides of the trunk, corresponding to "Application of Numbers" and "Cognition and Application of Fractions" respectively.

3. Draw several branchlets on the branch of "Application of Numbers", corresponding to different knowledge points, such as length, volume and mass unit. You can mark the corresponding knowledge points on the branchlets.

4. Draw several branchlets on the branch of "Understanding and Application of Fractions", which correspond to different knowledge points, such as comparison of fractions, addition, subtraction, multiplication and division of fractions, etc.

5. Draw a twig on "Understanding and Application of Decimals", and then mark the corresponding knowledge points on the twig.

6. On each twig, you can draw leaves or small flowers to represent the corresponding knowledge points.

7. Finally, you can write the words "knowledge tree" at the bottom of the mathematical knowledge tree as the general title.

This drawing method can clearly reflect the relationship between knowledge points, make students better understand and remember each knowledge point, and provide important learning reference for students.