Thanks for your patience, this may have been a stupid question in the beginning, but I found the solution I was looking for. I will make some brief descriptions here so that friends with similar problems can solve them faster.
First, the problem I want to solve is how to emulate diodes in CST. In the beginning, ADS was used because the manufacturer only provided ADS models. Taking a detour here, I think ADS can help me generate SPICE files. (such as .cir and .net, which can be accepted by CST) In fact, if you want to apply the SPICE model in CST, it is best to find a product that the manufacturer provides SPICE for design, so that you don't have to build it yourself, hahaha.
Secondly, CST has certain requirements for acceptable file formats, and we should pay attention to the following points:
(1) The .lib file provided by the manufacturer is used to define the device. CST needs a .cir or .net file, which is used to describe the circuit file. The .cir file can be implemented by directly modifying the file suffix.
(2) After modifying the file type, it is necessary to define a sub-circuit, which only contains a diode. (Note that two ports are defined.) For example:
.subckt subcirA 1 2
...
.ends
(3) In the CST version I use, the .cir file is required to have the same name as the defined subcircuit (this may be the basic knowledge of SPICE, I don't know). For(2), that is subcirA.cir.
(4) Give a complete example:
.subckt subcirA 1 2
D1 1 2 Diode A
.model DioadeA D
+is=15E-15
+n=.9
.ends