The Chinese zither, or Guzheng is tuned to a particular set of notes, called a musical scale. This tuning helps gives the Guzheng its musical character and sound. Let’s learn the names of the strings on the Guzheng. The most common scale it is tuned to is the D Major Pentatonic Scale – Spelled D E F# A B
Guzheng players also associate these tones with their Solfege names – D is Do , E is Re, F# is Mi, A is Sol , B is La.
Here is an excerpt from Bei Bei’s Guzheng Tutorial:
On the Guzheng this pattern of notes – D , E , F# , A , B is repeated over the length of the instrument. It is an important to note that the thinnest string and the thickest string are ‘D’ strings. The instrument starts and ends with ‘D’ strings. To help the eye see this pattern the “A” string is usually another color , mostly green but sometimes red. 
It is important to relate the tones of the D Major Pentatonic Scale with the notes of the D Major Scale. The D Major Scale is Spelled D E F# G A B C#. The D major Pentatonic scale omits the 4th and 7th degress of the the D Major Scale.
Now that you have an understanding of the names of the strings on the Guzheng perhaps you would like to continue with your studies? Bei Bei put together this Popular 3 Book Set to guide a total beginner into a well rounded Guzheng player. It is an excellent resource to even experienced players.