一面 … ，一面 … (two things at once)

Walk and talk — the written pair

• one side一面yí miàn … ，one side一面yí miàn … = doing two things at the same time (= one side一边yī biān…one side一边yī biān…).
• one side一面yí miànto walk走zǒu，one side一面yí miànto make a telephone call打电话dǎ diàn huà = "walking while making a phone call."
• More formal / written than one side一边yī biān…one side一边yī biān….

one side一面yí miàn + V1，one side一面yí miàn + V2

• one side一面yí miàn…one side一面yí miàn… runs two actions in parallel.

he他tāwhile一面yí miànwalk走zǒu，and一面yí miànphone打电话dǎ diàn huà。

• one side一面yí miànto walk走zǒu，one side一面yí miànto make a telephone call打电话dǎ diàn huà = "walking and phoning at once."

Recap

Read the full reference: HSK 5 grammar — Sentence patterns.