The difference between IIP3 and P1dB

The difference between IP3 and P1dB is usually between 10 - 15dB.

Does this mean that the amplifier has a good linearity? Or the larger the difference, the better the linearity?

Could you provide relevant materials to explain it? Thank you!

IP3 has theoretically 9.6dB more than P1dB and it shows Third Order Intermodulation only.It doesn't mean the the amplifier is more linear or less linear..
It's the problem of differences of the Nonlinear Transfer Function Coefficients, that's it.Some components may have higher than first kind, some others may have lower then first kind etc.
As a rule of thumb , If the system will amplify one single carrier, P1dB is more important.Otherwise higher IP3 is always preferable.

Theoretically, in a real life, P1dB is more important than IP3, because IP3 value is an imaginary point (never reached) that indicates when the amplitude of the 3rd order products equals the input signals; when P1dB actually is a real measurement of the compression point which shows when the distortions in the amplifier occur. Usually the amplifiers should be operated below the compression point.
Anyway, (also in a real life) the 10dB difference rule (between P1dB and IP3) could be easily broken (up or down) by the design of the amplifier, especially by the bias filtering design of the amplifier.